More Avengers 4 guessing here. Partially based now on the info from those leaked production photos being discussed, so spoilerizing that part:
I suggested earlier that the plan in A4 could be to go multiverse-hopping looking for the stones to power another infinity gauntlet to bring back to our universe and fix what Thanos did.
It’s been teased before that Pym particles and Ant-Man are the keys to the multiverse, so it sure seems logical that’s what’s going on. Specific to the scene being discussed in New York, I bet those are our Avengers crashing the Battle of New York in another reality with the intent to take the gem from Loki’s staff when they’re finished.
I know the Dr. Strange stuff in Infinity War could strongly be hinting at time manipulation being the key to fixing things, but I’m still leaning toward alternate universes being the answer, not time travel. I think the time gem was just important in letting Dr. Strange set things on that course.
And that’s at least partially due to my hope that somehow, somewhere, we still get basically a “what-if montage”, glimpses of different realities where they can provide a whole bunch of fan service without actually turning it into multi-year commitments. Like, as much as I love both Bucky as Cap and Falcon as Cap, even if their contracts are a lot longer than Chris Evans’ contract, I sort of can’t imagine either of those two wanting to stick around long enough to do those arcs justice. But if we’ve got realities to hop through, we could just have some quick scenes in a world where Bucky is leading the Avengers, or even—dare I dream—Luke Cage is leading the New Avengers? The multiverse angle lets you throw in the fan service they’ve made clear is impossible otherwise, it’s the only way I think we’ll ever see anyone from the television side of the universe on the big screen. Daisy could be running S.H.I.E.L.D.! Hawkeye could be married to Mockingbird! Time travel doesn’t open up those possibilities the way the multiverse does.
But that’s all still a long shot, I know. Just dreaming out loud.
Also, I don’t think Captain Marvel will be the lynchpin of AV4. I think the stinger in Infinity War was just in the vein of all stingers past, it’s a quick nod to what’s coming next. I expect Captain Marvel will be in AV4, certainly, but I don’t think the whole thing will come down to her involvement.