OP here.
When I started building this a year and a half ago, this was my plan. Since then, (1) there has been an explosion of note apps and (2) I realized that I do not really feel enthusiastic about building out commodity features needed for that. Instead, I am slowly building for myself, experimenting with different ideas and workflows[1], and sharing them on my blog, with the hope that someone else picks them up.
Alternatively, if I wait long enough, the "note app" part will become a commodity itself, and I can implement the interface/workflows on top of it. Quarto[2] looks promising in that regard. Their visual editor[3], which is used in R Studio, is really good.
[1] As an example, I at some point played around with a zooming user-interface: https://twitter.com/ichverstehe/status/1347896632424198144
[2] https://quarto.org/
[3] https://quarto.org/docs/visual-editor/