I think fractal designs are the way to go! My favorite notetaking app is Workflowy which does this exact thing with nested lists, and it supports boards too! One thing I would suggest is that it needs to be possible to "peek" at lower levels; it's a bit jarring to drop a card on another card and have it completely disappear. It's not immediately obvious that the card actually went "inside" the right one.
Thank you, yes fractals rule the world (literally?). Seen Workflowy, didn't use it, but it looks rather easy to use. And final text is readable. It's important.
I plan to add view/export of board as a text, so it can be read as a whole.
