Implementing what? It would be a copy of the current store, just with a much higher crap volume. Hell, they could even take 50% of the price of the apps for the crapstore.

They'd have to add a second data source in iTunes (a config file most likely) and probably unhardcode some URL's in the backend to the appstore where they hardlink to things.

Additionally, they'd have to make a copy of their appstore app and point it at the crapstore.

There are so many things wrong..... So, let me got back to the most important numbers in computing 0,1, and many. Transitioning any software from one of those numbers to another is generally a pain in the rear and requires a lot of testing, programming, and resources.