The Hollywood Reporter notes that the AVENGERS film would unite Iron Man, Captain America, Thor and Hulk, which might be the first time that Hulk’s inclusion was mentioned in an official capacity. Though that could be pure speculation on their part instead of actual fact. That said, I think I’d love to see Hulk make an appearance. The Ed Norton (excuse me, Edward Norton) version of HULK was a great movie and that version of The Hulk should absolutely be involved in any AVENGERS movie.
As for Gregg and his Coulson character, I’m guessing he won’t have a whole lot to do in THOR other than to make SHIELD’s presence felt. My only question is, will this be the only cameo we have in THOR? Will Sam Jackson or Robert Downey, Jr. show up? Or will they have cast Captain America by then and be able to sneak him in?