That Spider-Man will be joining his fellow heroes of the Marvel cinematic universe is a minor miracle worth celebrating. While his inclusion in the films was never in the realm of the impossible, it was thought by most to be pretty unlikely. Hollywood is a silly, complicated place, but in the end, money has a way of making complicated situations less so.
Whether they liked it or not, at the end of the day, Marvel needed Spider-Man to appear in these films eventually. Had they got to the end of Phase 3 with no Spidey involved, everyone would have understood, but it still would have been weird. It would be like DC making a universe of films with no Superman; they may not be at the same power level, but they're both the stars of their brand.
The side effect of all this is that the idea of Marvel bringing in other characters they sold the movie rights away to way back when doesn't seem so far-fetched anymore. Just imagine Hugh Jackman as Wolverine going toe to toe with Captain America.
No, seriously, imagine it. Because that's the only way you're going to see it happen for now.
Marvel has a good thing going. They've taken known but not necessarily hot characters and made them into icons. They've taken characters that most of the public didn't even know existed and made them into household names. They've made stars out of a wisecracking raccoon and a tree that says only three words. Marvel is the best there is at what they do.
And yes, they did this without Spider-Man, Wolverine or the Fantastic Four. These are all characters who have been integral parts of the Marvel comic universe, characters who would have been welcome additions to the Marvel cinematic universe...five movies ago. Changes have been made that make certain appearances just too difficult to bring about.
Spider-Man always had the easiest path to the screen. With all the other heroes they'll be launching in the next few years -- Black Panther, Doctor Strange, Captain Marvel -- it would be silly to say that sliding in the story of a teen who learned a valuable lesson about great power and great responsibility after being bitten by a radioactive spider is difficult. Sure, the world probably doesn't need yet another Spider-Man origin story, but introducing him to this universe should not be particularly difficult.
Wolverine is a whole different can of worms. He's a mutant, for one, and adding mutants to the cinematic universe has been rendered moot by the fact that Marvel is going full steam ahead with the Inhumans, who are a different group of folks who, like mutants, look like humans but aren't quite humans and have superpowers. (Broadly speaking, of course. The whole mutant thing is far too broad for the scope of this blog. Moving along...) The cinematic universe, with the time constraints that come along with the fact that they are movies (and television shows), doesn't really have the time to properly explain and explore the world of mutants. They just don't fit in with the plans.
As for the Fantastic Four, the only member of the group that would add anything to the cinematic universe is Reed Richards, and between Iron Man, the Hulk and the rest of the planet, they're pretty well covered on scientific geniuses. He would be a nice addition, but ultimately kind of redundant.
Not to mention, the fact is that while fans think they want Wolverine in the Marvel movies, they really don't. The stories would not be fulfilling in the way that the comic stories have been. The Avengers don't really need another abrasive loudmouth on the team; they fight enough among themselves as it is. Would he be a better option on the team as opposed to Hawkeye? Well, yeah, of course, but that's not how things shook out as the story developed. You work with what you have access to, and Marvel had Hawkeye.
The Marvel movies, as fun as they have been and as funny as they are, don't really lend themselves to the other type of Wolverine appearance we'd all like to see: the wacky team-up. Yeah, we all want to see Wolverine and Rocket Raccoon on screen at the same time, but that sort of silliness just doesn't work for the big-time storytelling going on with the Marvel flicks.
Of course, this is all thinking in the present. It's not impossible that Wolverine will eventually be in a Marvel movie. It might be a decade or so before it happens, but consider this: These are comic-book movies we're talking about. At some point, Marvel will get to the end of the story they're trying to tell, and they'll reboot the entire universe. There will be new actors in the roles of Iron Man and Captain America and Thor, the pages will be blank for new adventures and everyone will know how much money stands to be made.
In that scenario, I can absolutely see Marvel making a play for the X-Men. Get the mutants involved from the start, and you have all sorts of interesting scenarios for Phases 2 and 3.
It's just a shame that Hugh Jackman came along 20 years too early. He's so good at being Wolverine that it's an actual shame there's just no room for him in the Marvel movies at the moment.