What I try to do for my application, all offline features are free and features that talk to the backend are paid. Of course that won't work for every type of a

What I try to do for my application, all offline features are free and features that talk to the backend are paid. Of course that won't work for every type of application. The idea is that only paying customers generate any cost (aside from bandwidth to serve the application resources). For example, full-text search would be paid features, while a simple search that can be done reasonably on the client would be free.