They will probably announce it during the invitational. Highly likely GC controller support will be added. I mean its already supported right now but not properly recognized.
I don't think the GameCube controller is the be all end all, just the previous 2 nintendo generations had atypical controllers which were not ideal for a fighting game. For the first time in a while nintendo has a normal primary controller with the dogface or handheld configuration. The pro is a bit better though
I.. personally don't like the GameCube controller, the face buttons are just wtf in a bag, A being massive, B being pimple sized, then x and y being small pills haphazardly placed