Assalamau Alaikum

I think Ibn Qayyim al-Jawziyya believed that unbelievers will come out of hell eventually. I have not read it, but you can search online for this article

"Islamic Universalism Ibn Qayyim al-Jawziyya's Salafi Deliberations on the Duration of Hell-Fire"

It was published in the magazine called "The Muslim World", in January 2009 by Jon Hoover

Ibn Qayyim al-Jawziyya is not a small or fringe scholar.

In these two verses in the Quran

One day will He gather them all together, (and say) "O ye assembly of Jinns! Much (toll) did ye take of men." Their friends amongst men will say "Our Lord! we made profit from each other but (alas!) we reached our term - which thou didst appoint for us." He will say "The Fire be your dwelling-place you will dwell therein for ever, except as Allah willeth." for thy Lord is full of wisdom and knowledge.

Those who are wretched shall be in the Fire There will be for them therein (nothing but) the heaving of sighs and sobs
They will dwell therein for all the time that the heavens and the earth endure, except as thy Lord willeth for thy Lord is the (sure) accomplisher of what He planneth.

God adds "except as Allah willeth" in these two verses. So it might be that Allah Wills to end the presence of unbelievers in Hell, but that is only based upon his wills. And in the verse following God says,

And those who are blessed shall be in the Garden They will dwell therein for all the time that the heavens and the earth endure, except as thy Lord willetha gift which shall never be cut off

In this verse God also says "except as Allah willeth" but adds, unlike the verses for Hell, that this Garden, so Paradise, is "a gift which shall never be cut off." It is a nuance also worth pondering upon, as people of both Hell and Paradise will dwell therein, but in the case of Paradise, and only Paradise, God mentions that it is "a gift which shall never be cut off."

Then we can note that the recompense of an evil is just its equivalent. I do not know how this fit into the "supposed" eternity of Hell, but this is something to think about, as the words "Abada" , "khaliduna", "Ahqab" that are usually translated as eternity for the duration of Hellfire, could indeed mean eternity, as well "as very long time" in arabic.

Read those verses

QURAN
The recompense of an evil deed is its equivalent.....

Whosoever shall come with a good deed will gain good there from; but as for any who shall come with an evil deed - they who do evil deeds will not be requited with more than what they have done.

Whoever shall come with a good deed will gain ten times the like thereof; but whoever shall come with an evil deed will be requited with no more than the like thereof; and none shall be wronged.