I won't shed any tears if it doesn't happen because there is a cost (probably 2nd rounder) and a risk that comes with it. If he gets injured we pretty much wasted a 2nd. The reason I liked the idea of him being on this team is because he is an impact player. No single defender, no matter how good, is going to do much for your overall defense. You need multiple impact players on defense to make a real difference. We have a few right now, Lee, Lawrence, and who knows which others may step up? We may have more than we know right now so I thought E.T. might fit in well.
As far as him being out for himself, at some point in your career you have to be because no one else will. He's aging and he knows he's not getting another contract from Seattle. He's doing the only logical thing at this point in his career. It actually benefits both sides if Seattle trades him during their rebuilding stage.