This is an interesting roundup of different developers feelings on transitioning to a subscription-based monetization model. I'm doing that with one of my apps and am curious to see how users respond. All free features will stay free. Some new features will be free. Some new features will be with a subscription only. I bet I get plenty of people complaining. I currently get emails occasionally calling me greedy. My app and all features are free. You can donate if you want. Such greed!
I do think Kyle Howells has the best description of why users get mad about subscriptions. The platform is set up for them to expect lifetime free maintenance and upgrades.
Grief From Transitioning to Subscriptions compiled by Michael Tsai