The best model I know is the one used by Sketch (https://sketchapp.com/pricing/ https://sketchapp.com/pricing/): A year of updates. A lifetime of Sketch

The best model I know is the one used by Sketch (https://sketchapp.com/pricing/ https://sketchapp.com/pricing/): A year of updates. A lifetime of Sketch Your license comes with a year’s worth of updates. Once that year is up, you can keep using the last version of Sketch you downloaded, forever. * You can always open the files you have made * There is no incentive for feature creep caused by having to "sell" the next version to your current userbase every so often. * The developer does not have to keep supporting old versions forever.