Yeah, I actually expect some third-party Mii costumes in the next wave. Probably from Bandai Namco, Capcom or Sega franchises.
I do wonder if they'll do some kind of cross-promotion between Smash and Project X Zone considering the companies involved in both games...
Has the site been slow for you since the upgrade? If so, make sure to drop by the Forum Support section to report the issue.
As for rumors, there's only the Shovel Knight one. There were a bunch of pictures posted on 4chan, but already proven as fake.
Still,
Tama
's rumor has yet to be determined as true or fake.