I got a reply e-mail...it was indeed a technical problem on Nintendo's end, and has been fixed.
As for the game itself...I just spent an hour with it, and there's really nothing left to do far as I can tell. I won all three matches (though the last one took some practice), and even found a weird easter egg (hint: it involves Doc's chocolate bar)! Good, but short. It does make me want to get back to playing the retail Punch-Out!!, which I never finished, so that's good, right?

