To be clear: Org format is just plaintext, and you can use it mostly in the same way you use Markdown. It's nowhere near as popular, but if all you want is Markdown feature parity, then there is growing support in other editors and places. It's only when you want to go beyond Markdown that this becomes "Emacs or the highway".

Biggest difference for me is, that I had already been taking notes in markdown since before I heard about it. The only change for me was the welcome relief of not having to be creative any more about what headings or links should look like. Rest of the syntax I already used because that's how I've always made text files "look good".

As for your orgmode example, it's not a very good example of "just plaintext" if the metadata code in between the bits of text is larger than the content of the note. I imagine that with nice syntax highlighting it becomes easier to parse in just a glance, but then it's no longer "just plaintext" in the same way that e.g. YAML isn't.

It probably works very well, but to me it looks a lot like a plaintext encoding of a database record or something. It's a different use case. Not a simple note that is "basically plaintext". For instance I would not feel entirely comfortable editing your example without worrying I'd mess up the structure or produce a syntax error. Though maybe the format is really forgiving, I can't tell. What happens if you forget the :END: bit, for instance?

You can certainly write org in ed, if you're masochistic enough. You could also use Vim or VSCode or whatever floats your boat, and you will just be missing the more useful stuff (agenda integration, babel, etc), but if you just want to use it as a markup language, there's good support in other editors, and ease of export as well (pdf, html, docx, odt...) with pandoc. I don't get why you think that editing org is any harder than editing markdown, given editor support.