With the Circle Pad Pro accessory the 3DS has should cover those who want a C-Stick feature (but since I'm so satisfied with the controls of Cartoon Network: Punch Time Explosion, the next Smash won't encourage me enough to finally buy a Circle Pad Pro).
Anywho, for the Wii U game, as long as it supports the Wiimote + Nunchuk, Wiimote held sideways, the Classic Controller, Wii U GamePad, and the Wii U Pro Controller with the option to totally customize the controls like Brawl did, I don't see any problems with the controls in the next Smash. And since the Wii U Pro Controller has everything the GamePad has minus the screen, it wouldn't matter if we can't buy more than one GamePad.