Re: New Mutants
In the eyes of the mainstream audience, it was a prequel and it is still a prequel to this day. They even showed clips from the OT in the trailer of FC, so there's no way they would have seen that as a prequel + Hugh Jackman's cameo.
And of course, FOX could haven given First Class, the title of the 1st of the prequel series/trilogy but now that they brought back the original cast instead of just releasing a 2nd film with the cast of First Class. Things have changed. For me, the appeal of doing a First Class trilogy is gone when they brought back the original cast.