I think the idea that it'll be PS3 exclusive in Japan, but have a 360 port elsewhere, makes the most sense. Now, this may be a load of crap and I have no idea what I'm talking about, but there are plenty of BB players in the west who don't own both systems and only a 360, whereas that is definitely not the case in Japan. They would not lose much money from not bringing it to the 360 in Japan, but over here, that would cut down on a sizeable amount of profit and would alienate a lot of the fanbase, especially since not everybody who plays BlazBlue is going to buy a brand new system just to play the next game(I admittedly would). This would hardly be the first case of "PS3 only in the east, both consoles in the west" occurring, too. Now, if we get an official release date for America and there's no mention of the 360, THEN I think we should be worried about it there.
Of course, it what I just said is all bullshit and I'm talking out my ass, then I'm sorry for the confusion and/or acting like I know what I'm talking about.