Turned out there were performance problems on larger notebooks but its pretty smooth now. I got the pinning working so it will remember open code cells on export... sometimes the code is the content so you can have the runnable code of certain cells open by default. Sometimes the content is the content and then an inline editor for markdown* makes more sense and not bothering with a code editor for writing prose. Very good. Its quite nice now. Properly built in dataflow and in userspace, so if you change the canonical code editor its instantly reflected in the clones. There a tons of small functional and navigation bugs to fix. Biggest next thing to tackle is not losing all your progress when closing a page and forgetting to export (a.k.a. change history).