Didn't read the other posts, so excuse me if someone has said this.
But has anybody else thought that it may be Vince who joins with Legacy? I mean, from a kayfabe standpoint, Shane is the owner (Stephanie saying he can keep running the company, she'll run the show a few weeks back) but now Vince is back, so Shane is not needed. Vince comes down in the No Holds Barred match and joins up with Orton, thus Vince vs Shane II at WM 25.
As for, why would Vince do that, he is the puppet master. Shane is the puppet.