I have a theory for Infinity War, sort of. I guess I should say **********SPOILERS************** just in case, even though it's just a theory. So, here goes...
A couple of things, really. The first relates to the last infinity stone (the soul stone). It's hard to not fall into the "find the McGuffin" mode of thinking when we've got so many installments and we know it is all leading up to a quest to find and, depending on which side you are on, either unite or keep separate the six infinity stones. I've given my opinion in the past that I think it makes the most sense for it to probably show up in Ragnarok. I recently read a new theory about how and why it shows up in that film, and based on what we know about Ragnarok, it makes perfect sense and seems pretty likely to me. And, no, it isn't the Heimdall theory, although he does tie into it. Google "the last infinity stone has been hiding in plain sight" if you want to know more (and I quite like the pun involved in that wording). If true, that theory makes a lot of sense. I think it would be smarter for Marvel to hold off and actually not introduce it until the first Infinity War film. It kind of makes sense that that first film would be all about the race to find it. But I think it may very well end up being in Ragnorok instead. I guess we'll see.
The second thing is, I think Nebula is going to play a major role in Thanos' ultimate defeat. I know she's a fairly minor character. But her character took on a much larger role in Guardians 2 than I would have thought, and that kind of seemed out of the blue unless it is for a larger purpose. Guardians 2 also made me realize a couple of things about her relationship with Thanos: she hates him; she has a relationship with him; and she is motivated. She's also not very competent, however, and makes dumb decisions based on her emotions, so there's that. But it just seems to me that she's in a good position to be overlooked and to throw a monkey wrench into his plans. It would also seem somewhat poetic if it wasn't actually the Avengers that took him down, but a lesser important character that enabled his defeat. I dunno. I could be way off on this, but the thought occurred to me, so I thought I'd share it.