Thats what I did/will be doing with my old expense tracking app, Amounts. It was a paid app only, some 8 years ago before subscription apps were a thing. 3 year

Thats what I did/will be doing with my old expense tracking app, Amounts. It was a paid app only, some 8 years ago before subscription apps were a thing. 3 years later I moved to free + a singular IAP unlock, existing users were grandfathered in. Now I am doing a complete rewrite of the app for fun on the side, and moving it to a subscription. All existing paid users will have the full subscription unlocked. I also built in a smooth data migration process so they retain all their existing data and functionality. I'd estimate I have about 50 or so long term users from app store install stats, as I didn't have any analytics in the old app. Sadly, for larger companies loyalty to the customer base doesn't make financial sense, when you can make $$$ from new users, and your old users just cost you money to support.