There are quite a few unconfirmed rumors blasting across the Internet. Not sure I want to get into all of them but one caught my attention.
You may already have heard that Tony Stark (Robert Downey, Jr.) and Pepper Potts (Gwyneth Paltrow) are planning a marriage at the beginning of 'Infinity War" (that wasn't clear to me when I saw the movie the first time). They are, of course, interrupted by Dr. Strange (Benedict Cumberbatch) and Bruce Banner (Mark Ruffalo).
So
BGR published a little more information about that scene, showing a clip of Happy Hogan (Jon Favreau). It turns out that Gwyneth Paltrow also let slip some time back that Pepper and Tony have a child. In the movie there is a scene where she tries to tell him something important and the call breaks off (because Tony is on a spaceship leaving the Earth's vicinity). Fans are guessing she was about to confirm his instinct that they were expecting.
One of the guesses that the BGR article makes is that Tony may leave the Avengers after the next film. There has been much discussion about the future of the team and the franchise over the last 12-18 months. Robert Downey, Jr. is (I think) the highest paid star in the franchise and he is probably ready to move on.
Chris Evans, of course, was notably signed to do only six pictures and people are wondering when he will leave the franchise. In the comic books Steve Rogers dies and other characters take up the mantle of Captain America. That hasn't played out in the cinematic universe the same way, so we're still waiting to find out what happens.
I may share some more rumors below. People are welcome to mention anything they find interesting. I don't know if any of these rumors should be considered "spoilers". A lot of things can be edited out of movies.