The only real missing piece is the audio I/O, but that is not too hard to do.  Ideally, the rjdj crew would release their audio I/O code to be included in Pd-vanilla and we should share the work of maintenance and improvements.  But that's not the only way to get it done.  I'm here at Mobile Art & Code talking with Memo Akten and Zach Gage, the two openFrameworks/iPhone developers, and they have open source audio code that should be pretty easy to plug into Pd.  SuperCollider has been ported to the iPhone too, but I haven't been able to find that code.