Since there's been no reply from the OP with his resolution or more information, I suppose all this is just a thought exercise, but IMO the Nevernever is like... tied to Earth, or possibly just humanity. I figure if there was a DFRPG game in space, we - humans - would bring the nevernever with us, but until we set foot on Mars, for example, there's no Martian Nevernever. Sure, there's probably some Earth NN place that's like the old pulp sci-fi Mars and the jungle-covered Venus of decades past, but those are there because humanity dreamed them, you know?
Winter and Summer have no meaning once you leave the planet. I like the idea of this, because it kind of takes the wind out of Mab and Titania's sails a bit. They're heavy, heavy, heavy hitter plot device NPCs, sure, but astronomically speaking they are just as insignificant as the rest of us.
All that said, if I had a player ask to be an alien, I'd have to consider it. The supernatural bleeds over into cryptozoology well enough, and once you're knife-fighting chupacabras it's not so far a leap to Roswell. However, I'd have to put the onus on the player to make themselves fit. "You want your special snowflake PC, I understand, but you make the little gray bastard fit into the setting."
I do like the fairies-disguising-as-aliens idea though. I'll probably use that in my game regardless.