If you get z-order perfect and would be willing to contribute it to the client itself and help with any somewhat confusing integration it would at the very least be allowed for developer tools which would make finding interface components and such much easier again. We used to have a similar overlay but had some issues and z-order has always been a problem. I assume you've made this windows only based on your JNA and if so that's fine, we would just have to check and only allow it to be enabled on windows unless you wanted to write the jna for osx and linux too. Regarding allowing it on general bots, it's up for discussion.
Arbiter just approved of adding a global client overlay if it works as well as you claim that would be usable by all bots with the condition that it's written using JavaFX to keep the embedded ui and overlay experience consistent
@Parametric