Actually my main point was that how the boundary between plaintext and markdown should be drawn? You might expect `>` as part of plaintext, but they are not IMO. Strictly speaking, the list character `-` also isn't plaintext. I would imagine converting markdown to plaintext is to remove all the "markup language" bit of it.

And I would still suggest you to try turning off all markdown extensions except for those you need, e.g. list and blockquote. You might start from markdown_strict which bundled with the least amount of extensions to keep your list short. I didn't try that, but I expect turning off all markdown extensions essentially making it plaintext.