The way they treated the incursions was odd. It seemed like a big enough threat to be the focal point of Phase 4, with all this multiverse tomfoolery threatening 616 with an incursion. Then the movie just had Strange turning up in universes suffering an incursion and being incredibly blasé about it.
In the Thor thread, it seemed like this phase has set up a lot of super-powerful cosmic beings and realms beyond imagining. So it seems like they could set up some sort of conflict between the heroes and cosmic (or “secret” ) conflicts (or “wars” ) with the most powerful beings in the cosmos coming together and deciding that the heroes are just making too much of a mess to the universal order.
And then we discover that all these threats from Thanos to Galactus to Ego were the machinations of some cosmic adversary (or cabal of them) – as well as the sudden emergence of superpowered beings on Eart in the open within the space of a decade is the equally enigmatic counter-plan of some potentially more benevolent cosmic beings that want to help us without exposing themselves to the big bad.
I also like the idea that there is something inherently weird between the “magic” side of the Marvel universe and the Science side. When it starts to get to the “Cosmic” realm, there is some kind of synthesis between them. Sorta like the idea of Green Lantern where they are this super-science corps of the most archetypal SF pulp heroes, but their rings and lanterns all run on magic. By the way, they should be called the Green Ring Corps. Why would you advertise the fact that you have to charge the damn thing up every day? That’s a potential vulnerability!!
There could be an interesting idea that the “One Above All” created science and magic as an evolutionary tool and those races that synthesize them eventually advance into Cosmic beings. However, the cosmic beings that have evolved to the pinnacle of the Cosmos take a look at humans and start to think “are these our replacements? Better just nip that in the bud.”
The eternal beings like the celestials, eternity, the Watchers and Galactus (and on and on) form a sort of order, but the next generation of super-people, particularly humans on Earth, are beginning to have the power to upset that order — and there are certainly other very powerful beings that have an interest in both eliminating the humans or on the other hand, to help them upset the order so they can grow even more powerful. The heroes’ allies might not be heroes themselves.
Besides, it would be cool to see a rogue Watcher Uatu really go hog-wild with his powers fighting to save the Earth! Not something you might see in the comics, but the movies should do it.
EDIT: Actually, thinking it over, ROGUE WATCHER would be a great Marvel comics series. You could do the star-spanning SF space opera route with the watcher crossing the universe and using his powers to face off against massive extraterrestrial threats, but I think a simpler, down to Earth (literally) and partially comedic approach could be a better hit.
Cast out of the Watcher Corps for breaking their one rule “watch everything, do nothing”, Uatu wanders the world like Caine from KUNG FU and uses his powers to help those in greatest need. However, he can’t be too open about it, because there is another Watcher overseeing the planet’s history, so Uatu has to secretly help people to seemingly help themselves.
Eventually, though, he suspects the new Watcher is not so disinterested in the events of the planet and has schemes against the Earth, so Uatu secretly conspires against this new overseer. However, he has to be careful, because if Uatu succeeds in exposing and dismissing the new Watcher, his former brothers might want to give him his old watcher job back, and that would be a fate worse than death.
If it was a TV show, I’d cast Rainn Wilson or Nick Offerman.