Hello Serif!
At first let me thank you for your awesome products! I really appreciate them.
Next, I'm well aware of fact that it's been while since you started selling Affinity Photo and Designer. So probably your income flow slowly decreasing. Not sure about current state but it is expectable soon or later. Many companies choosing strategy create new major version or start using SaS strategy. Both variations have its upsides and downsides. Both are however quite complicated strategies because people doesn't like them. For people who doesn't need more than they have now but need compatibility with new OSes this means they have to pay for new version which may even introduce some problems. However pay annually is mostly unloved by users who use this app mainly for hobby projects.
There are two another monetisation strategies that I believe are better.
1. Optional paid functionality.
New version of app will remain free update to all who purchased previous version but new features will be optional in-app purchase. This way users might decide if they need new features or not. Professionals will probably pay while amateurs who need only basic will keep happy with what they already got.
2. Optional contribution
Show users who use Affinity often (fex: more than five days in week) a small dialogue that if they will contribute some money, the upcoming updates may stay free for all. It's kinda "optional SaS" strategy based on beloved brand which you probably want to become and which you, I believe, already became.
Those are my thoughts on topic that users usually doesn't want discuss until it's already late.
My best wishes and thanks.
