still awaiting on a Wii RPG maker game from Enterbrain. I know it can be done and except for doing dialogue, the controls would suit perfectly for everything else a RPGmaker can do.
Dialogue shouldn't be too tough, since the Wii has supported USB keyboards in recent firmwares. At least in the Channels, but I'm pretty sure if it supports it in the channels, games should be able to use it too.
Still, I'm not sure I'd like a Wii RPG Maker as much as I'd like an XNA-style homebrew suite for WiiWare.