UPDATE 6/14: And they're out! They're $0.75 a piece or you can buy the 3DS/Wii U bundle for $1.15. The eShop is all kinds of crazy at the moment. Patience!
Original story: A day ahead of Nintendo's Super Smash Bros. direct, data miners have extracted two new Mega Man Mii costumes from a patch added to the game’s Japanese servers. So pretty soon, it looks like you can trick out your Mii to look like Mega Man.EXE and Zero (X series, no less).
The full details of the leak can be found on Gematsu and NeoGaf. We'll be learning more about this content tomorrow!
Thanks for the tip, Brandon and Christopher!