Yeah, so I think I kind of figured out where Hawkeye is. It’s no secret he’s been missing from Infinity War promotional material, but I’m pretty sure that the reason behind this is… He’s being held captive on a Skrull Warship! Now hear me out. During Civil War the Skrulls infiltrated his home and replaced his wife and kids. Catching on to this, Clint embarks on a solo mission to rescue them, and discovers a much larger scheme, a secret invasion. He finds his family, but before he can escape, he is captured by the Skrulls and being held captive.
It lines up with everything the Russo Brothers have said. That he’s on a personal quest and it’s a long play and a spoiler. Also the set photos of him in the Ronin outfit help, since he was using that alias during the Secret Invasion arc and he probably doesn’t want to be associated with the Avengers, or, you know, get arrested since he doesn’t wear a mask.
This will also segue into the next Avengers movie, which, since the name is supposed to terrify us, would probably be Secret Invasion. Because Captain Marvel will have come out by then, introducing us to the concept of Skrulls, and what’s more terrifying then figuring out that none of our heroes are who we thought they were? Well, that’s my two cents anyway!