StarJammers could work, but I don't see it as 'Fox's GoTG' nor do I think Fox will rush to do it at this point, because it will be seen as emulating GOTG.
For space stuff, Fox has Avatar.
I think some cosmic elements could work, though. Starjammers needn't be a standalone project. They have two choices - make it entirely separate and not even bring in the Corsair link at first, or tie it firmly to the X-Men series. Making it entirely standalone does look a little like a copy of GoTG.
I don't think Fox 'emulating' Marvel is necessarily a bad thing. Samsung is a successful business venture that emulates Apple.
Also, I don't see why Fox can't have two franchises that deal with "space stuff". They once had Star Wars and Alien.
As far as the choices you've given them, wouldn't making StarJammers a completely separate film without the Corsair link be unwise for them? Given that they
can link it to X-Men, without the film overtly being an X-Film, not linking it seems like a missed opportunity. Your other option of tying it firmly to the X-Men would work, but again, from a business standpoint, if you can have an X-Men film one year, and a Starjammers film another, with each being independently successful at the box office, that makes more sense than to just make one.
^ Agreed. I think they'd be smart to just tie them into an existing X-Men movie, especially one where Phoenix is involved. I think that'd be a lot easier to help expand the X-Men universe.
Fox has a lot of other untapped X-teams and franchises that I think should be top priority such as X-Force, X-Factors, New Mutants etc.
I would love for a proper Phoenix X-Men film with the inclusion of the StarJammers, but given the way the Phoenix was explained in the 3rd film, it would be a hard one to pull off. Plus the studio probably wouldn't allow for that same story to be retold given all the other possible stories they could tell. Now, if they introduced the M'Kraan crystal, and introduced the Phoenix force that way, a it's protector, then that could work. I think that story would work best as a standalone StarJammmers film.
I do want X-Force, X-Factor and New Mutants films, but there's no reason they can't make those AND a StarJammers film.