I'll point you to the FOSS work I do [0] so that serves your point #3. As for #1, that's an inherent limitation with the APIs. As for #2, it depends on the economics. Most such tools (NetGuard, TrackerControl) are available free of cost with an option to sponsor the project. From experience, I can tell that no one really sponsors or donates.
[0] https://github.com/celzero/rethink-app