That was just one of many, most of which simply can't be done as iPhone apps (and several of which already exist for Android).
Well, the very first thing that I wanted to implement was something like this:
http://code.google.com/p/android-scripting/
1. Interpreter/VM with arbitrary code.
2. Open Source
Until recently, VOIP was banned, as well.
Aside from decent notifications and real background tasks (and the aforementioned Locale, which was also on the list), the biggest blockers are the App Store and its restrictive policies.