Theodore of Mopsuestia (Bishop of Mopsuestia from 392 A.D. until his death in 428 A.D.)
"The wicked who have committed evil the whole period of their lives shall be punished till they learn that, by continuing in sin, they only continue in misery. And when, by this means, they shall have been brought to fear God, and to regard Him with good will, they shall obtain the enjoyment of His grace."
Source: Bibliotheca Orientalis.
Hans Urs von Balthasar (Roman Catholic Theologian):
I do not wish to contradict anyone who, as a Christian, cannot be happy without denying the universality of hope to us so that he can be certain of his full hell: that is, after all, the view of a large number of important theologians, especially among the followers of Augustine. But, in return, I would like to request that one be permitted to hope that God's redemptive work for his creation might succeed. Certainty cannot be attained, but hope can be justified.
Source: Dare We Hope That All Men Be Saved?: With a Short Discourse on Hell (Ignatius Press, 1988), p. 187 in most printings.
And again:
"The question of a possible conversion of the demons is not possed by revelation. It remains a purely speculative question. Dogma leaves it open. In this matter, then, we are free to hope, just as we are free to hope for the salvation of all men."
Source: Dare We Hope That All Men Be Saved? With a Short Discourse on Hell (Ignatius Press, 1988), pg. 221-222.
Pope Francis
"The Good Lord will save all of us, but don't say that too loud."
Source: https://wherepeteris.com/universalism-and-hell/
Pope St. Paul VI
Since reconciliation means the restoration of peace both between God and man and between men themselves, it is the first fruit of redemption. Like redemption, it is universal in scope and efficacy. It reaches out to the whole of creation 'until the time of universal restoration' (Acts 3, 21), when all created things are again unified in Christ, Who is the firstborn of the risen dead (cf. Col 1, 18).
Source: https://wherepeteris.com/pope-st-paul-vis-exhortation-on-reconciliation-in-the-church/
Ambrosius Autpertus (An 8th century Bennedictine monk, abbot, and Theologian who wrote commentaries on Holy Scripture.)
Rev 20:10 “And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are: and they shall be tormented day and night for ever and ever (Latin: saecula saeculorum)." But when it says, "they shall be tormented day and night for ever and ever (Latin: saecula saeculorum)," it is not to be taken in such a way that no sentence of God’s mercy is left at all: but because very long times (Latin: saecula saeculorum) are appointed for punishments, which human frailty cannot measure. It can happen that even the evil spirits themselves, who are now obstinate in their wickedness, after very long times are freed by God’s mercy, when they put off the nature which they corrupted, and are reformed to that for which they were created. But if this is so, it does not detract from divine justice, because they will have paid for a very long time what they deserved.
Source: Ambrosius Autpertus--Commentary on the Apocalypse (c. 784 AD), Book 10, ch. 36. Patrologia Latina 89:1391.
Agobard of Lyon (9th century Archbishop of Lyon)
"Nor should one despair of any creature made by God, that it could not return to a better state, provided it itself wills."
Source: Liber de Divina Psalmodia, Chapter 20
Clement of Alexandria (150-215 A.D.)
So he saves all; but some he converts by penalties, others who follow him of their own will, and in accordance with the worthiness of his honor, that every knee may be bent to him of celestial, terrestrial and infernal things (Phil. 2:10), that is angels, men, and souls who before his advent migrated from this mortal life.
Source: The Stromata (also known as Miscellanies), specifically in Book VII, Chapter 2.
And:
For all things are ordered both universally and in particular by the Lord of the universe, with a view to the salvation of the universe. But needful corrections, by the goodness of the great, overseeing judge, through the attendant angels, through various prior judgments, through the final judgment, compel even those who have become more callous to repent.
Source: Book VII, Chapter 12 ofthe Stromata (also known as the Miscellanies.)
St. Ambrose (Bishop of Milan from 374 A.D. to 397 A.D. Venerated as Saint by Catholics and Orthodox)
Our Savior has appointed two kinds of resurrection in the Apocalypse. 'Blessed is he that hath part in the first resurrection,' for such come to grace without judgment. As for those who do not come to the first, but are reserved unto the second resurrection, these shall be disciplined until their appointed times, between the first and the second resurrection; or, if they should not have fulfilled them then, they shall remain still longer in punishment until they have paid the very last farthing.
Source: Psalmum I Enarratio (Exposition on Psalm 1), section 36.
Also:
"When therefore, all things have become subject to Christ, through Christ's obedience, so that all bend their knees in His name, then He Himself will be all in all. For now, since all do not believe, all do not seem to be in subjection. But when all have believed and done the will of God, then Christ will be all and in all."
Source: Exposition of the Christian Faith (also known as De Fide ad Gratianum), Book V, Chapter 14, Section 181
Also:
"The mystery of the cross of the Lord is a heavenly thing; and it was wrought not only for men, but also for the angels. For those who are in the heavens may be confirmed, and those who are in the lower parts may be restored."
Source: De fide ad Gratianum (on the Christian Faith), Book I, Chapter 5 section 43.
St. Jerome
"I know that most people understand the king of Nineveh to be the devil, who at the end of the world—because no rational creature made by God should perish—descending from his pride, will repent and be restored to his former position."
Source: Commentary on Jonah
Gregory of Nyssa (Bishop of Nyssa from 372 to 376 and from 378 until his death in 394. Venerated as a Saint by Orthodox, Catholics, and Anglicans. Declared the Father of Fathers by the Seventh Ecumenical Council)
"Our Lord is the One who delivers man, and who heals the inventor of evil himself."
Source: The Great Catechism (Oratio Catechetica.)
Gregory Nazianzus (Bishop of Constantinople from 379 to 390 A.D.)
"These, if they will, may go Christ's way, but if not let them go their way. In another place perhaps they shall be baptized with fire, that last baptism, which is not only painful, but enduring also; which eats up, as if it were hay, all defiled matter, and consumes all vanity and vice."
Source: Oracles 39:19
Diodore of Tarsus (Bishop of Tarsus from 378 until his death in 393 A.D.)
For the wicked there are punishments, not perpetural, however, lest the immortality prepared for them should be a disadvantage, but they are to be purified for a brief period according to the amount of malice in their works. They shall therefore suffer punishment for a short space, but immortal blessedness having no end awaits them. For the penalties to be inflicted for their many and grave sins are very far surpassed by the magnitude of the mercy to be showed to them.
Source: Bibliotheca Orientalis.
St. Basil (Bishop of Cappadocia from 370 A.D. until his death in 379 A.D.)
We have heard before how many names of the Lord we have already been taught by the prophet. ‘Behold, a virgin shall conceive in her womb and shall bear a Son, and they shall call his name Emmanuel.’ Here His name is called ‘Messenger of great counsel’. He is the one Who made known the great counsel kept secret for the ages (Col. 1:26) and not manifested to other generations (Eph. 3:5). He is the one Who announced and manifested among the Gentiles His inscrutable wealth (Eph. 5:8), in order that the Gentiles should be fellow-heirs and the same body (Eph. 3:6) of Him whose sovereignty is upon His shoulder, that is Whose kingdom and power are on the cross; as having been lifted up on the cross He drew all to Himself (John 12:32). […] There is no end of His peace, for the reason that it is a supramundane gift. For had it been from the world, it would have lasted only as long as the world exists. But now, he who has accepted His peace and preserved it shall live with the good things of His peace for ever. The peace of Solomon was limited to the recorded years, whereas the peace from the Lord is co-extensive with the whole of eternity, being unlimited and boundless. For all shall be subjected to Him and all shall recognise His mastery, and when God shall be all in all (1 Cor. 15:28), and those making an uproar by their apostasies are silenced, all in peaceful harmony shall praise God with hymns.
Source: St. Basil the Great, Commentary on the Prophet Isaiah, translated by Nikolai A. Lipatov, p. 275-276
Theodoret the Blessed (Bishop of Cyrrhus in Syria from 423 to 457 A.D.)
"In the present life God is in all, for His nature is without limits, but he is not all in all. But in the coming life, when mortality is at an end and immortality granted, and sin has no longer any place, God will be all in all. For the Lord, who loves man, punishes medicinally, that He may check the course of impeity."
Source: Theodoret of Cyrus, Commentary on the Letters of St. Paul, vol. 1, trans. By Robert Charles Hill (Brookline, MA: Holy Cross Orthodox Press, 2001), 1 Cor 15:28.
Note: A Comment from a 6th century non-Christian, Pagan (neo-Platonist) Philosopher would appear of relevance to how the Greek words aionian, aionios, and aionas (commonly translated eternal or everlasting) were used and understood in the Pratrasic era.
Do not suppose that the soul is punished for endless eons (apeirou aionas) in Tartarus. Very properly, the soul is not punished to gratify the revenge of the divinity, but for the sake of healing. But we say that the soul is punished for an aionion period (aionios) calling its life and its allotted period of punishment, its aeon.
Source: Olnmpiodorus the Younger (AD 550)
And this quote from an 8th century commentary on Holy Scripture, shows that centuries later, even the Latin words used to translate aionios, aionian, and aionas in the Latin Vulgate were not necessarily understood to mean endless durion.
Ambrosius Autpertus (An 8th century Bennedictine monk, abbot, and Theologian who wrote commentaries on Holy Scripture.)
Rev 20:10 “And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are: and they shall be tormented day and night for ever and ever (Latin saecula saeculorum)." But when it says, "they shall be tormented day and night for ever and ever (Latin: saecula saeculorum)," it is not to be taken in such a way that no sentence of God’s mercy is left at all: but because very long times (Latin: saecula saeculorum) are appointed for punishments, which human frailty cannot measure. It can happen that even the evil spirits themselves, who are now obstinate in their wickedness, after very long times are freed by God’s mercy, when they put off the nature which they corrupted, and are reformed to that for which they were created. But if this is so, it does not detract from divine justice, because they will have paid for a very long time what they deserved.
Source: Ambrosius Autpertus--Commentary on the Apocalypse (c. 784 AD), Book 10, ch. 36. Patrologia Latina 89:1391.