Dark Elves: Not natural, but a race of elves changed by a curse.
Orcs: Again, not natural, but a race of elves so mutated they're almost not elves any more.
Dwarves: As of Morrowind, not actual dwarves in the traditional sense, but a race of elves that looks like they destroyed themselves
Ayleids: Mostly extinct after a huge war in Cyrodiil (I want to say almost genocidal). Might be totally gone by the time Skyrim rolled around.
And let's not forget...
Snow Elves:. Almost wiped out by Nordic ethnic cleansing. Betrayed and are now mutated in a far worse fashion than any Dunmer or Orsimer. Almost nothing but monsters now.
There's only two 'untouched' elven races left, Altmer and Bosmer, and they are tied up in this Thalmor/Dominion ordeal. I wonder where this is going.
The patterns I've noticed
1. With every new Elder Scrolls game, Bethesda introduces or focuses upon a previously unseen race of destroyed, mutated or generally abused elven race. With Skyrim it was Falmer. With Oblivion it was Ayleids. Morrowind had a 3-in-1 deal with Dunmer, Orsimer and Dwemer.
2. We're being carefully trained by Bethesda to hate the Dominion (Altmer and Bosmer).
3. The only other elven domain that had any kind of strength and prestige was Morrowind. Look what happened to that.
tl/dr:
If we do get a TES 6, which will be the new abused/mutated/destroyed elven race? Those Dominion guys aren't exactly doing a good job at making friends. All this makes me actually wonder (if even for a little bit) if Bethesda is looking to eventually do away with any Mer kind. It kind of looks like it, what with the way things are going.