I'm glad it's still in the "in basket." I suspect this is going to come down to a compromise between what-the-UI-should-be and what-the-tech-can-do, but I hope I'm wrong.

I've only seems something that's a little like this in outliners in the mid 90s, so having a working mockup would be really helpful. I look forward to more discussion! Happy to test anything or contribute how I can.