I love the opportunity this model provides. But for an existing app (that would greatly benefit from subscriptions and offers continuous new content daily) how

I love the opportunity this model provides. But for an existing app (that would greatly benefit from subscriptions and offers continuous new content daily) how to message this kind of switch w/o simply starting over seems, well, difficult to say the least. Unless you put one app "to bed" and start anew, how do others imagine taking advantage of this model? Or does it apply better to only new apps? Hard to say.