Messed around some more with #FlaxEngine researching what it would take to implement some things particular to my project. Overall, the editor seems very performant (at least with my silly test project), but a bit glitchy. I was able to do what I needed to do (mostly), but both the editor and GUI API are a bit limited, not well documented, and have some frustrating behaviors.

Later I'll try out Godot for a bit.