I've noticed that betting against Marvel Studios is a fool's errand; every time they decide to do the impossible (crossover all their solo movies into one blockbuster, tell a space opera about a tree, raccoon, and Han Solo fanboy saving the universe with a magic rock, cross over all their franchises into one two-part epic with insane expectations, and make B and C list characters beloved superstars), they usually succeed on all fronts. So, if Kevin Feige things he can do the X-Men justice, he has the resume to prove that he could pull it off (heck, this guy was able to diagnose everything that went wrong with the ASM2 movie before it was finished).
Let's see, Feige has gone on record for seeing the Raimi Spider-Man movies as examples of superhero movies done right, knew the flaws with the Mark Webb ones, and oversaw a good reboot of the property that had some exceptional villains, acting, and stories. Hulk's proven to be a good supporting character. That's all actually very encouraging. (Wasn't Feige involved in some of the Fox X-Men movies, too?).
Which is his right.
The "Marvel formula" is a myth. That is a simple fact (don't believe me; watch the frakking movies). It's time to let it die and focus arguments on actual stuff in the series itself (like maybe weak love stories and villains, or how substantial changes are kind of rare).
There's more to the MCU Spidey movies then that. In fact, Far From Home has been pushing the character in new directions and setting up stuff never done before. Can we at least give the devil his due?
Days of Future Past, sure; they've got the chops for large team stories and emotional story arcs; they could do it. Logan, maybe not, but do we need a MCU Logan? (Also, I'm not sure you really get what "adult" means; "adult" has nothing to do with a lack of color, comedy, and hope. Heck, some of the most childish stuff in the genre was grimdark, had lot of violence, muted, colors, and people who never cracked smiles or were ever happy -- you know, like real human beings. The Guardians of the Galaxy films are some of the funniest, most comic booky movies out there, but, if you actually look at the story and themes, there's complexity there on the level of Logan. Hint: watch the characters' stories, not the glitz in Guardians or the gore in Logan. That's where real maturity and adult themes are found.)
The X-Men had their share of wacky sci-fi, stuff, too (killer robots?). It's fair game and most of the really out there MCU movies are out there by artistic design. (Also, what about the Captain America movies?)
Dunno, the original X-Men movie had toys. Heck, I'd pay for Marvel Legends figures of the Fox X-Men characters if they made them (and the X-Men: Evolution show, for that matter -- and no, not just because I want Cyclops and Rogue figurines as alternative wedding cake topper options to Spider-Man and Mary Jane in case I ever got married, thank you very much ). They're currently making Funko Pops of the original X-Men movie characters, too...
Like they did in the First Class movies (and Beast's old uniform in X3)? Why was that okay, but the MCU embracing the color wasn't?
Seeing as we don't know a thing about what Marvel Studios has in mind, it's a bit early for doom and gloom; at least know what it is your're damning before actually doing it.