I think at some point they will reveal that Miis still have costumes, and they will announce several most wanted characters who didn't make it in the game as Mii costume, similar to what happend with Smash 4's DLC.
Also, we know nothing about the other modes, and stuff like collectables, stage editor, etc. so they will most likely move the focus on that stuff.
They will probably reveal all the characters very soon, since they need to send the copies of the game at stores and it would be way easier to spread leaks once the game has been sent everywhere, especially if all the characters are drawn on the box for real.
IMO we have less than 2 months before we know everything about the main roster, maybe 1 month before the actual release we will know everything already, officially or not.