I'm not sure I understand the point of your (2). If it means that you can't add functionality, then how can that functionality be added via an app in (3)? And

I'm not sure I understand the point of your (2). If it means that you can't add functionality, then how can that functionality be added via an app in (3)? And if the functionality could be added via a script in (2), then would there even exist a market for the app in (3)? It seems like your sequence really should be: (1) Make a platform that doesn't do everything. (2) Sell apps to cover missing features. (3) Improve your original operating system, rendering paid apps useless. And that'll always work, at least until your operating system does do everything.