I think touchscreens and development go together well, but perhaps not in the way you're imagining. The best thing about a touchscreen is that generating any symbol is equivalent in complexity to generating any other. Unlike real keyboards, which have fixed symbols in fixed positions, a virtual keyboard can be as large and complex as you want—if you run out of space on one "layer", you can just add another set. This would make a language like APL perefect for mobile development, especially if combined with some manipulable visualization of the resulting parse tree (I.e. What most visual PLs try to be.)
I think the real problem is input. Would it be enough to have a "hacking mode" software keyboard? Or would it require a physical keyboard at this point? Would the current iteration of physical keyboards even work? I've not used a Droid keyboard, but they have nice screens and I'm sure setting up a dev environment would be a lot easier in android than on the iPhone. That is to say, possible (sans jailbreak).
This is a cool idea.