If they ever do then it needs to be a major storyline than any side quest. Maybe as an enemy threatening to take over Nirn in a "war of the world" type storyline with Dwemer instead of aliens.

I can't see them returning as a playable race. There are other races such as Akiviri humans (if they exist), Maormer, Sload, Akiviri snake race etc who I'd rather see first. I like the Dwemer as a mysterious race of the past. It adds interesting lore to TES. I'd want to see the Admeri wars and hopefully get the visit parts of Akavir before any chance of them returning.