According to lore, Argonians may be able to change gender. There is no concrete evidence of this. It is speculation based on the language they use in reference to gender. But given its scope, ESO could potentially answer this question.
Personally I like holes in lore to be filled in, mysteries to be solved etc. So I'd find it interesting to discover the truth of this in ESO. And the idea of players being able to change gender has so many possibilities. Imagine the fun you could have with Argonian drag names?
Could be controversial though. I like that the ES games have a fairly progressive attitude towards sixuality. But I wonder what the kinds of groups who objected so loudly to SWTOR's "gay planet" would do with something like this.