[ryannielsen]

As a developer with apps in the MAS, this sounds like a sales, maintenance, and support nightmare.

How would you architect your app to have separate, modular features?

How would I reliably test all combinations of all features?

How do I properly advertise app functionality without deceiving users?

How do I properly support users when they have issues? (Depending on what they've purchased, they could have a very unique set of features and UI enabled.)

You're taking a hammer and using it to tighten a screw. Instead, Apple should be offering the proper tools we need to offer reasonable app upgrade paths.

[msbarnett]

It wouldn't, necessarily, have to be excessively modular.

Say, one in-app purchase, the "2012 Feature Pack", or some such.

That said, I'm not convinced its a better idea than just creating a new FooBar2 app in the store and pushing an update to FooBar1 advertising the launch sale of the new version.