Bradley Cooper, during an interview with MTV for his new film Burnt, got a bit confused about Guardians of the Galaxy characters, but may have revealed one actual piece of information about the sequel. In the video, he tries to dance around things, but can't seem to remember the names of any characters in the movie, exacerbated by an interviewer who thinks she's getting major scoop and tries to lead him down the wrong path.
If you don't want to watch the embarrassing video, here's the gist: Cooper drops the possible spoiler that Thanos is "the main villain," though he uses his presence in the first film as an example, saying he was the "main villain" in that one. He also thinks Thanos is Ronan's dad (and the interviewer in turn thought he was talking about Star-Lord), so he's not the perfect source of information on this stuff.
Incidentally, ComicBook.com has first-hand information that the final script for Guardians of the Galaxy Volume 2 may still not be completed, at least as of a couple of weeks ago. Dave Bautista told us that when he visited with Gunn three weeks ago, he was offered a second draft, but didn't want to read the script until it was finished. Vin Diesel received a copy of the script and posted about it on social media, but we can't confirm whether it's that second draft or a now finished and approved version.
So, in the end, Bradley Cooper assumes that Thanos is the main villain in Vol 2, but that could mean as an over-arching villain like in the first film, or as a more hands-on bad guy. So, he seems to know as much about we do (or less, since we know Thanos isn't Ronan's dad). It's okay, Bradley, just keep using that voice of yours to make Rocket a lovable a-hole and that's all we care about.