Fox's track record with X-Men looks kinda like this to me:
X-Men (2000): Great
X-Men Origins Wolverine: Okay (very middle-of-the-road)
First Class: Good (almost a return to form)
The Wolverine: Poor (not as insulting to our sensibilities as X3 but just boring as hell and pointless)
So two complete duds, one that people don't really care about and the rest are either good or great. Here's what we can learn from the good ones:
-Faithfulness to the source material is good so STOP FUCKING WITH CHARACTERS LIKE DEADPOOL AND JUGGERNAUT please.
-Wolverine is just not interesting enough, power-wise at least, to head his own movies without massive attention on cameos or co-stars and not just humans, but mutants.
-Need side characters to make things interesting in general BUT don't overdo it like X3.
As for F4, I think the biggest problem has been Doom. Never has he been portrayed the way he is in the comics, where he's just a completely normal human who has such technological mastery and domination over an entire nation that he's capable of dominating the globe if left unchallenged. There's no way the F4, in a self-contained world, could possibly be a threat to him. So fusing the two universes of X-Men and F4 is the way to go. Let Doom have some long-range plans involving a robot and mutant army, and force the F4 and X-Men to team up to stop his evil plans. Surely even Magneto would get involved if it meant mutant liberation was at stake. Plus then cosmic threats and the like could be handled more easily. The X-Men bring the powers the F4 don't have and Richards brings the space travel tech the X-Men don't have. Truly if there were two properties NOT in Marvel's hands right now that could complement each other perfectly (aside from Spider-Man and the X-Men; gotta love when the web-head teams up with Wolverine) it is the X-Men and F4. Like I said, if they're bringing the current X-verse to a close, the ill-advised F4 sequel should simply be scrapped and rebooted as a crossover with the X-Men. Honestly, they could do with some recasting anyway.
I do agree with one of the guys from AMC movie talk, though, in that if every property belonged to Marvel again, we'd never see most of these guys on the screen. Granted that does mean we're going to get cinematic turds sometimes due to Marvel's parent company not being in charge of their productions but...universe willing, these other studios will pull their heads out of their asses and learn from their mistakes. Sony took remarkably long to figure out to ask Marvel for help so they stop raping Spider-Man, and we still don't know how that's going to work out. Fox is officially batshit crazy if they do move ahead with the F4 sequel and fail to ask Marvel for help in doing it right next time.
I really wish there were sublets or whatever kind of thing would work so that the main Marvel studio wouldn't have to divert too much attention or budget cash but that some of their less-popular but still worth making characters can get their movies. Maybe have them in a timeline parallel with the MCU but detached so that unless the main films call for it, these others wouldn't get too involved (kind of like how Daredevil season 1 was). That way Ghost Rider, Namor and others could get some screen time and not have to wait a decade to appear again.