Your favorite idea has literally hundreds of possible customers!
#5 mystified me.
I had a vague wish for XCode on my ipad.
haha scary....
The trouble with an IDE for the iPad is that it can't include a compiler unless it's only for jailbroken devices (which severely limits your market). I'm convinced there would already be several if Apple didn't impose that limitation, but an IDE without the ability to compile or run tests is kind of a hard sell.
What if the code is compiled remotely? If it's a web app, that makes sense because you could then view it in a browser. Of course no compilation necessary for rails and it's colleagues.
Xcode already has distributed compilation support. I've never used Visual Studio, so I can't comment on if it has support or not. Either way, a cloud-like compiler 'front-end' might be a decent idea, as long as you factor in the CPU costs involved. Compiling C family languages is a rather intensive task.