I'm inexperienced in this side of the lore. However, I'll still ask- is it possible for a tower to have two stones?
I can't help but think of the creation of Nirn here and with that thought, the Mundus's creators: Magnus, Lorkhan.
The visionary as well as the heart of nirn's ideals. Eye of Magnus, Heart of Lorkhan. Aren't those names so convenient..
I don't think it's possible for a tower to have two stones; there's no establishment of that, and we tend to hear about a stone that anchors a tower instead of stone
s.
Correct me if I'm wrong, but isn't the wheel a tower because all the kalpas are their own wheels all stacked on top of each other?
In that case, the universal stone would have to be something that transcends kalpas.
I believe Vehk states that if one looks at the wheel from the side, it appears as "the one and only name of God; I".
As for a universal stone that transcends kalpas; my best guesses would be either the Elder Scrolls themselves (since they can show all possible paths, destinies, timelines, etc.) or the Godhead. The only true way to "end" existence would be for the "dream" to cease and for the Godhead to "awaken", so to speak.