The only one I'd like to see be used in a future Elder Scrolls game especially as a playble race are the Maomer. Make it so sometime in the 5th era the Maomer re-enter the world scene and start trading with the other races and some have started living on Tamriel.
As for Skyrim DLC and only in a Skyrim DLC make it so the Tiger folk of Ka'Po'Tun from Akivir invade and we the Dragonborn have to defeat there leader the Tiger Dragon. However make them come to us do not make us ever go to Akavir. Leave that continent mysterious.
I've thought about something. Their leader, Tosh Raka, is actually (Or were the base for...) Akatosh. How you may ask? Well...
Tosh Raka
Raka Tosh
Aka Tosh
Off topic: I made a topic about it before but nobody seemed to care too much. I think this is not a coincidence, as Tosh Raka turned himself into a dragon. Akatosh is usually drawn and described as a dragon so it makes sense to me. So what I would say is Akatosh is a divine, but furthermore the people of tamriel (somehow) thought Tosh Raka was a god and worshipped him. The worship continued on for so long after he went they don't even know how they started it, and then started to worship the actual god (Akatosh, who is not to be confused with Tosh Raka but he is the origin). Anyways, this is off topic. Since I don't think bethesda had actually written lore for this yet (since they probably made that name up so people would come up with theories like bethesda do for many things to keep fans busy) I would still say this is the best/closest (in my opinion) we can get.
But yeah, that was off topic. I'd also like to see Sea Elves as you said though, I'd more preferebly see Dwemer, as there is not too much about Maomer, but then again, there isn't too much about Ka Po' Tun, either.
Edited by AlienSensei, 06 March 2013 - 07:26 PM.