I'm not a big fan of traditional text formatting because of all its problems, like having to preserve it during copy/paste, having to think about own save format, and so forth. This adds complexity and bugs, and you have to maintain it.
While not using formatting, I still need to organize my text for readability, so I use simple techniques like stars (*) for bullet lists, line breaks to separate paragraphs, something to highlight headings and so on. Now this is very close to using a lightweight markup language. What they are doing is define a "standard" set of such simple techniques. Your raw text will always look fine, but you can additionally present it with rich styles by using extra renderer.
The idea is to have two modes: raw and rendered for both notes list and note editor. Editor in rendered mode could apply styles on-the-fly similar to how Confluence editor works.
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