Ah, thank you! It looks like Agenda[0] does use that model. Here's a blog post with details[1] in which they mention that Sketch[2] also uses the same business model (with some minor variations).

tl;dr: you buy the app and 1 year of updates. You keep what you pay for.

I wonder if it would be viable for an app like photoshop to have a feature marketplace. You start with a very basic version of the app and you buy the features you want piecemeal. You then have a separate service contract for ongoing support (ie: bug fixes).

[0]: https://agenda.com/ [1]: https://medium.com/@drewmccormack/a-cash-cow-is-on-the-agend... [2]: https://www.sketch.com/