It's only been a "big possibility" since the end of last week. Before that, most sources reported that Bayern was in the driving seat, due to Bayern's statements that Vidal had agreed to join them. And then you had Arsenal, Chelsea and Man United, whose fans all have been pretty optimistic of landing this fella, I've checked out their forums.
As for who opens a thread, I couldn't give a rat's ass, but ... I suppose it is rather "symbolic", when BD has been right all along, that he be given the opportunity to open a thread, if it means something to him.