It is rumored that the Maormer, or commonly referred to as "Tropical Elves" are going to be a new playable race in TES Online. Whether or not this is going to be a playable race in future elder scrolls games as well is unknown at this point.
Maormer are not rare, but tend to stick to their homeland Island Pyandonea, which is off the coast of the Summerset Isle. They are rarely seen in mainland Tamriel, which is probably why they aren't seen in any Elder scrolls games.
Snow elves may make some return in the future, but not anytime soon since there are no currently known villages or colonies of them. The snow elves most likely will not appear in TES:online, due to the fact that their race's extermination happened around the same time the Dwemer disappeared.
What are your thoughts on the idea of new races in the future of the Elder Scrolls?