If I were going to make a hard switch from apps I use (docs, sheets, todo, meet, ...), I would do so from the conviction I don't want vendor lock-in, and want to own my data. I like the concept. The Collection module seems powerful. Yet, I question the scalability - how long should users wait, for example, for a <tab> to be possible in a code block, in a notebook?

Since you're looking for feedback; - support markdown where possible, and include links like Obsidian, include Unicode completion like Julia REPL. Point and click is nice, but shortcuts/common syntax is expected, - support scripting via a modern language, - let users write plugins for modules / modules.