this would be great stuff indeed, but the restrictions you mention seem like a killer to me: you basically can't share any program that was written on this app. so how can this ever be more than a toy?
The previous generation had Amigas or whatever that was (sorry) they used to hack on. My generation had the early days of the web. This (and others like it) could be the next generation's hacking toy.
my point was that the technology exists to make sharing apps easier, but apps like this are artificially crippled by apple's app store policies, because they want to control everything.