Thank you for all these ideas, I will probably add most of them.
I have a good idea for customization : instead of just fonts, text, images... I will allow to load Godot scenes (.tscn) created by users. This is very powerful (even unlimited, you could use an entire godot game as a censor box xD), simple to use (especially when you can ask chat gpt "Create me a box.tscn file that do [the effect you want]" this works for simple scenes). The main concern would be security to load other people codes, but as it would be plain text (human readable) I think this is fine.
If you start Hotscreen from a command line, you will see that it output the new detections : name, score, position/size on the screen. It can probably be sent to an AI that you can prompt to react from this list in real time.