This is an Elder Scrolls roleplay, with the 
Redguards (black warriors), 
Nords (tundra warriors), 
Imperials (politically and economically inclined), 
Bretons (magically inclined), 
Altmer (High Elf- magically-inclined), 
Bosmer (Forest- dunno, never seen any in Skyrim besides a few), 
Dunmer (Dark elf), 
Orismer (Orcs, brute warriors), 
Argonians (lizard marsh people), 
Khajiit (cat desert people), 

and then those extinct/twisted 
Dunmer (underground elves, or dwarves), 
Falmer (twisted versions of the Snow Elves- only one exists as a regular Snow Elf, that I know of, in Skyrim), 
Aldmer (the original elves, who knows where they are), and 
Maormar (Sea Elves).

The entire world and lore of the Elder Scrolls is already written out, and continues to be written. The lands, though, it's all taken- your new Dark Elves or whatever wouldn't fit into anything. They'd be... no one. I doubt he would let you bring an entirely new race into the mix, where you could easily merge it to the already existing Dunmer/dark elf. He was wary of me adding my vampire, much less a new type.