I absolutely agree, subscriptions are the way to go for making your software business sustainable and better scalable R&D investments to maintain growth. Gitlab is an example of this in the dev tooling space.

I've bought Mailplane v3 for my Mac a few years back. The app did not get new features, only patches. New features came out with v4, which required another purchase. I didn't buy it because v3 is good enough, buying again is a psychological wall. If it was a subscription I'd be happily paying them and happily using the latest version.