Well, there were stories flying around this summer that he was offered $100 million to do four more movies...and those were quickly shot down as false, with Hugh saying that if he'd signed a contract like that, it would sound he was just doing them for tons of money instead of doing them because they're going to be good movies, and he didn't want to do things that way. It's basically what he's saying here, too.
James Mangold did a Twitter Q&A today, and mentioned as much as he could about the sequel...which obviously isn't much (the person asked if we'd see Omega Red next), but it's at least an indication that things appear to be moving forward.
@amazon_movies: @MNzHussain Too early to tell you that MNZ. I've got something in mind but too soon to tell. Suffice to say that everything's on the table.
I can't see Hugh not doing it...as long as it works with his schedule, and the story is good, I imagine he'll be back.