They can make good movies based on Marvel properties (sometimes, they are 5 for 11 at best), but they don't know how to make them faithful to the source material.
I'm not exactly sure of the rights situation, but I truly do not see the FF and the X-men crossing over anytime soon. That's a pipe dream.
Anyways I have no interest in studio wars, it is petty and boring and I don't want to stir the pot any further.
Also the "alternative" you speak of is this movie failing, Fox realizing they don't have the capabilities to make a good FF adaption, and selling the rights back to Marvel. That's what an overwhelmingly large percentage of what the fanbase wants, and it's an idea that won't go away any time soon.