The guy from Inkdrop [0] makes a living with his note-taking app. He also has a YouTube channel [1] which I found very relaxing.
Also needs to pay for the cloud servers running it lol.
I don't see anything wrong with this. Users buy software because it solves their current problem now, rather than a possible feature in the future. The revenue stream is definitely more reliable though. Just that as a user I wouldn't mind if the software I bought today stays that way forever, and as a developer I wouldn't mind developing software to completion then leaving it as that.