I think this is very interesting. I'm going on a trip for a few days today and was thinking if there were some way I could tinker around with arduino code on my mobile while away and here's the solution :).
Would it be possible to have a simulator running so I can test my program directly on the browser? It doesn't have to be visually pleasing, a simple text dump of the sequence of events and what's happening with each of the pins should be a good start. Perhaps with time you can also add basic components like LEDs, resistors etc and popular ICs like 595, 555.
I use Proteus to simulate all my arduino projects before I even put them on a breadboard. Something similar "on the go" would be awesome.