Fox doesn't care about FF. They just simply don't. If they did, they wouldn't have waited until the 11th hour to get it made, made it on the cheap (or at least tried), nor have been radio silent the project; not even officially announcing the cast until the end of last year.
And most importantly, provided the rumors are true, they wouldn't have been trying to sell the F4 rights back a just over a month before filming began.
The sole purpose of this film being made was to keep the rights from reverting, until a time they can sweeten the deal for giving them back. Whether its a success or not is neither here or there for Fox, because they can't cross it over with the X-Men franchise and, due to Trank's vision, it doesn't look like building a franchise off this film is in the cards, despite the fact the already scheduled a sequel; which means nothing in this day in age, considering THREE sequels to ASM2 were scheduled and official announced, and they'll likely never see the light of day.
This film is serving its purpose for Fox. And that is simly to hold to the rights. Nothing more, nothing less.