In Morrowind/Bloodmoon the "insane" guy with the skull prediction an invasion from Oblivion.
Hence predicting the next game in a way.
Ever met the insane Bosmer down at Anvil docks, talks about his mother coming to rescue him in the dragon ships.
And a bunch of other Akaviri invasion related things that I cannot recall exactly at this moment.
Though that is true, dialog in Oblivion (in the form of rumors that appear in random conversations) also hints at trouble in Black Marsh and speaks of Daedra worship becoming increasingly prevalent in the Summerset Isles and a boycott of Imperial goods in the same province, these sound no less likely, if not more so, to be hints at the plot of the next Elder Scrolls game than the ravings of a seemingly mad Bosmer.
God I hope not. Not another completely inhuman outside invader!
If they are still humanoid mortal races with behavior and personalities resembling humans it is not so different from the premise of Morrowind's plot, really, except for being an inside threat rather than an external one. After all, Dagoth Ur is by no means human, never was, and I would say that any race from Akavir is more human than his servants, at least they are mundane races instead of horribly mutated monstrosities.