The thought has definitely occurred to me. It's always been in the back of my mind on the "if it shows some success..." list. Glad to hear there's interest, I think it would be really fun if I implemented proper multi-touch. There are some other details I'd need to think through, though, since right now it mostly assumes you have a MIDI keyboard, but on an iPad it's just begging for touch controls for a lot of that stuff.
Amazing, I do all my music on an iPad simply because if I open my laptop work will materialise. Now that I've put the idea in your head though, I think it's probably my duty to warn you that the market is a tiny fraction of the desktop market.
I'd focus on ipad & an awesome multitouch experience. App store sales are easier & i'd bet apple would spotlight it.