For 25 years, Image Line have been shipping the FLStudio DAW as a one-off purchase with free lifetime updates, and since I've been receiving those updates for a significant chunk of those 25 years since I bought the Producer Edition, it seems pretty sustainable.
In their words "Why? Because we believe you should get the program you paid for, bug-fixed and updated for as long as we develop FL Studio." [1]
In their words "Why? Because we believe you should get the program you paid for, bug-fixed and updated for as long as we develop FL Studio." [1]
[1] https://www.image-line.com/fl-studio/lifetime-free-updates/