Then I took a week off of work to focus on the editor. I hate UI work and the only way to get past it was to just get in done. The key to getting it done was someone on the #bevy discord directing me to a discussion on the github about implementing egui widgets as SystemParams: https://github.com/bevyengine/bevy/discussions/5522
As of today I now have an infinite hex grid shader in #bevy , with the current cursor position highlighting. Sharing source code because it's always helpful to have an example: https://github.com/dmlary/bevy-hex-grid