The news here is that Spider-man will basically lead into the aftermath of the Infinity War, if I am reading this correctly. So perhaps some of the regular characters will die off and then there’s a shift in who is leading what. This is what Feige had to say about why a Homecoming sequel is the perfect film to kick off the new version of the Marvel Cinematic Universe:
“So much happens in [the 3rd and 4th Avengers movies], as you can imagine, and so much is affected by it that we felt what better person to hold your hand and lead you into the next incarnation of the MCU, in a grounded, realistic manner, than Peter Parker? So, coming out two months after Untitled Avengers, [that’s what] much of what the next Spider-Man film will be about.
It was purposefully done like this. Like how the events of Captain America: Civil War impacted Peter as he was dropped off by Tony and expected to go back to continue his sophomore year, how the hell are the events of Infinity War and Untitled [Avengers] going to affect him as he, yes, goes back to his junior year?”
One thing is for sure: Robert Downey Jr. isn’t getting any younger, and neither is Chris Evans. While I can see them playing their respective roles for a few more movies, perhaps until Downey is in his fifties, I don’t see them going on much longer, so I suspect either an MCU reboot, or a culling of the herd character-wise, sooner rather than later, and the events in the upcoming Infinity War are pretty much perfect for that happening.