Also I have a piece of hardware I bought from the Astropad folks and if the app suddenly stops working because they demand a subscription I'm gonna be pretty damn unhappy.
Part of the problem, of course, is that app stores have completely killed "upgrade pricing". There's no good way for your existing users to give you money for "hey we added some new features and fixed some bugs" without bullshit workarounds like "okay the new version is a totally new app, go buy it".