The Towers and the Thalmor
This is, unabashedly, me putting on my most exquisite tinfoil hat and theorizing what I believe to be the goal of the Thalmor in the Elder Scrolls universe.
Spoilers for all the major Elder Scrolls games, I think?
So, what do the Thalmor want? According to the loading screens in Legends, and the Infernal City by Greg Keyes, the Thalmor wish to subordinate all other peoples of Tamriel and "bring about a new Merethic era".
I find this somewhat lacking as an overarching goal. Simply taking control over Tamriel is something that the Cyrodiilic empires of Alessia, Reman and Septim have tried, and to varying extents, succeeded in before. Subjugating the other races seems a little bit on-the-nose. So what instead? What do they mean by bringing about a new Merethic era?
Well, the beginning of the Merethic era is considered the introduction of the Adamantine Tower to Mundus, and the beginning of linear time at the Convention. There, Lorkhan was punished for his treachery in creating the world, and by his execution, two more Towers were formed, or at least their essence was implanted in Mundus: the Red Tower and the White-Gold Tower, alongside their respective stones, the Heart of Lorkhan and the Chim-el Adabal, the gem at the center of the Amulet of Kings.
The Towers that formed after the Adamantine Tower was placed (or flown onto, or constructed on) on Nirn, seem to be the origins of the differences between the elves, what allowed the Bosmer and Chimer and all the other mer to distinguish themselves from the Aldmer, and later the Altmer. Condsidering Crystal-Like-Law is meant to be a copy of the Adamantine Tower, I personally theorize that the Altmer are in fact closest to what the Aldmer were like before the sinking of Aldmeris.
Thus, I think that "subjugating" the other races is less about subordinating the other elven races under the iron fist of the Thalmor and the Aldmeri Dominion, but more about forcing them to revert to a more Aldmeri state, in essence making all elves return to their pre-sinking of Aldmeris forms. The humans and beastfolk might simply be subjugated, though.
But I think it might even go further than that. I think the end goal of the Aldmeri Dominion is nothing less than the un-creation of Mundus. Notably, I don't think the goal is merely destruction, as Alduin or Satakal might aim for, but the undoing of the very creation of Mundus. In essence, undoing what Lorkhan tricked the Divines into doing.
The Altmer give us the terms "Aedra" and "Daedra", meaning "our ancestors" and "not our ancestors". I think the goal of the Aldmeri Dominion is to return the stolen strength and power of the Aedra to them, power which is used to maintain the constant that is Mundus, and which allows for linear time, and to return the elves to a state where they were indistinguishable for other et'Ada, other powerful ancestral spirits.
To do this, the collective strength of all elven nations might be required, which would explain the conquering tendencies of the Aldmeri Dominion and the Thalmor, while also giving a reason for the seeming destruction of the Towers around Tamriel.
So, how far have they gotten? And what is the final act?
Well, which Towers are operable?
Crystal-Like-Law - Seemingly inoperable, according to "Rising Threat", but might still be operable in other planes of existence.
Red Tower - Probably inoperable, considering the destruction of the Heart of Lorkhan by the Nerevarine, but might simply need a new Stone.
White-Gold - Inoperable, as the Chim-el Adabal is destroyed.
Orichalc - Unknown, thought inoperable with the sinking of Yokuda.
Snow Throat - Likely operating.
Walk-Brass - A conundrum. Thought inoperable, might simply need rebuilding and a new power source.
And the last Tower. The site of the Convention, Ada-Mantia. Likely operating, considering linear time continues on Mundus, this is, in my opinion, the final goal for the Aldmeri Dominion. To destroy or disable Ada-Mantia and break the Earth-Bones which bind the Aedra to Mundus.
My sincerest hope for the Elder Scrolls 6, aside from re-introducing spears, is that the Adamantine Tower becomes an important site for the plot, if it truly is set in the Iliac bay region.
This has been a cathartic embrace of my inner tinfoil hat-wearing lore nerd.
I'm probably wrong (for canon), but I love the Elder Scrolls, and I will head-canon this always.