Earlier quoted context omitted.
This. When working on your own engine you also feel as if 90% of the time is spend on user interface creation if you actually want to have an visual editor. People don't realize that they will spend 95% of the time on the engine and 5% on the game. Which is ok if you don't want to make a commercial living out of it. But unless you are making a game with extremely specific needs (eg Factorio) using your own engine wil…
Visual editors are a waste of time. For 2D, lots of solutions exist (Tiled for example). For 3D, you can use Blender as your editor. The key to making no engine work is to make only what you actually need.
I have limited experience scripting Blender, but there is a BPY API to add custom panels, so adding metadata to “entities” and simplifying the export workflow is probably feasible to the point it will be very close to an editor.