Captain Britain

[Phil]

It's very much blown out of proportion.

The original tweets from the costume designer didn't mention Netflix at all.

If it's genuine (and that's a BIG IF - especially this close to April Fools Day) it's most likely a TV show from Fox who own the X-rights and are currently making TV shows based on Legion and The Hellfire Club.

Captain Britain isn't a mutant, but he's probably more closely tied to the X-Verse than the MCU, through his association with Excalibur and Psylocke's retcon to be a mutant.

As to AF; it's still up in the air.
Department H was listed in screen grabs for X-2, but also mentioned on Agents of SHIELD.

IF Marvel/Disney were to own the rights they wouldn't be able to use Northstar & Aurora, or at least not as Mutants. (Though I'd rather they weren't used at all, than be Elves).

So basically, we won't know till we know!