I currently use Emacs Org mode for my zettelkasten knowledge system, which uses .org files (I use this plugin: Introducing Zetteldeft). I had originally used markdown, but it has several issues and inconsistent versions which led me to switch to .org. It seems that many developers with zettelkasten systems have also chosen this setup.
I love the UI and Vim keybindings for Obsidian and would love to try it. It would be awesome to have support for .org files (or at least a way to convert them) in addition to markdown.
Yeah, using org mode has some nice additions such as expanding/collapsing large sections. But I agree that it encompasses a lot of functionality so there would probably have to be a lot of interested folks for it to make sense.