'It's my first python & Kodi project too so I'm no wizard. I wanted to look into this feature again after I investigate the new settings system in Kodi 19.
I think the new system might make it easier to come up with a settings UI that supports this. The original implementation I got the colour logic from (ScreenBloom) supports dynamic zones based on X,Y points in a dict. I think the best implementation would be to keep this but adapt the settings to Kodi. Even if the settings UI wouldn't really let you have something fully dynamic, it could have multiple patterns like left/right, top/bottom, full screen. This would make it easier to maintain and easier to edit zones/patterns later on since only the settings would need to be changed and the code would be zone agnostic.
The other factor is performance. I don't know how expensive the crop method is, but at a minimum, if someone isn't using zones it needs to skip that for speed.
For now, I didn't make a start on using the new settings systems since Kodi 19 doesn't support the
Pillow Image Library that's needed to manipulate the image yet. I didn't want to implement something I know I'll be changing in a couple weeks/months.'
I think, you've made a lot of work already and, please, don't stop.