On Miis, for me they don't have to have a customizable moveset as I feel like they could offer enough without such option. Miis (or the concept of creating an avatar) has a long history with Nintendo -- in a way you could almost call them historical.
Now, I'm indifferent about Miis. If they get in, however, I do hope they're unique and fun as much as possible. I don't want to argue on their pros/cons because that's not the point I'm trying to make.
Going back to what I said before: on the history thing I recommend watching this video if you haven't before:
I may not care that much about Miis, but seeing an idea Miyamoto had struggle to find its place around 20 years ago and evolve into the successful Mii concept that we have today is kinda inspiring. And Miis are still going strong and probably will in the future.