This is just brainstorming, not a finished product. I initially suggested the Storm Elves as a race, but they said that having three Elven races would be too much, so I combined them into one larger race. I was thinking about something else at first.
For level 4, a Pegasus; level 5, an Elf-Sniper (he's a sniper because he also shoots lightning with his shots); level 7, a Storm Dragon. I still need to think about the others.

First, we need to come up with all the logical races, and then we can propose additional ideas. It's right to say that a Swamp faction with lizardmen is needed, but it's already been cut down so much that it will be difficult to create. Next, the Dungeon – not Elves, but the second legitimate underground race – troglodytes, trolls, medusas (more correctly called gorgons), beholders, manticores, etc. Then, of course, you could add elementals, but that's unlikely... given Ubisoft's canon and rules...

Now it's time to come up with the most optimal options – the much-discussed underwater race, the evil mages (like an Ice Castle with ice dragons)... and then you can add at most one more Elven race and various Khajiits, Gnolls, etc. :)