Nothing. It's just not Org-mode, and thus many great features of Org just not possible - sparse tree search; timestamps with built-in calendaring features; outline features like narrow-to-subtree; editing the subtree in an indirect buffer; executable code blocks; embedded LaTeX snippets; real tables with spreadsheet-like capability; checkbox statistics cookies - [/] and [%]; org-sort; column views; tags and tag inheritance; etc.
Anyone who's familiar with even a small subset of things that's possible in Org-mode and unlikely ever be supported in Markdown (just because there's no agreed format standard) have no confusion about it - Org-mode is absolutely superior. But superior doesn't mean universally better for everyone. The biggest drag of Org-mode is that it can never fully exist outside of Emacs. Yet Markdown can't ever fully cover its grounds (even in Emacs), simply because Markdown has to exist and work outside of Emacs as well.
So, you need to invent slots. Logseq did exactly that - all the org-mode specific lines get lifted verbatim into .md. Obsidian did it differently with emoji fields or Dataview inline fields (or whatever they called). Neither produces portable Markdown. GitHub renders those files as literal noise. The portability benefit that motivated the move evaporates the moment you add the metadata you need.
And then you'd have to build a specialized parser - there's no equivalent of `org-element` for Markdown. Sure, tree-sitter helps to some extent, but you're still lacking a semantic layer that turns nodes into records.
In essence - for Emacs to treat Markdown as Org-mode, we need to change Markdown, once that happens (if ever) Emacs can follow. But at this point it is already such a mess, it's crazy. Take front-matter alone - it's not CommonMark, it is a Jekyll convention that each tool does differently, and it is per-file, so your unit of thought is limited to become a file. That is the Obsidian/Denote/zk design, it works - but it moves your outline into the filesystem. You lose refile, subtree archive, narrowing, cut-and-yank of a subtree, and "this TODO belongs under that project heading". Org gives you both: file keywords at the top, property drawers on every heading, with inheritance down the subtree that front-matter structurally cannot express.
The point is that markdown could have todo's or virtually any other aspect that org mode supports put into it without changing the markdown standard and layer org functionality and various features on top for example todo's could simply be italic's starting with todo: so `# todo:todo hello` could be parsed as a todo entry marked as todo.
If you want to use markdown for Agenda and calendaring in Emacs you'd have to invent a different subset of markdown, most likely poorly supported anywhere else. And if you get there, then it begets a question - why? If we already have something far better and it's called Org-mode?
Since markdown is becoming so prevalent. Even our product managers are becoming natively conversant with it, I'd just prefer to have as markdown first world.
(don't get me started ranting about how Atlassian and Slack have migrated away from markdown and to proprietary formats....).
I definitely think markdown has won (at org was never going to 'win' of course given it's limited scope) and actually is probably what we should just all be using and accept.
- have it look through all md files in a directory, collect all the todos into a main view
- look for items tagged with a date
- support customer tagging, and provide workflow exports for each one...
- behind the scenes git management for files
- etc...
I've been wanting to build a collaborative markdown editor for awhile now, making it so that different front-ends could work with it is an interesting thing to think about....
Of course one might also want to actually build out todo nodes as CLOS style objects. Only caveat hear is that you would need to decide how the object should be serialized and deserialized and the deserializing has to be more precise.
serializing and deserializing to MD should be easy I think since all we need to do is read in headings and list items into lists with some denotation to the type it was.
Those are just my thoughts on the topic. My thinking has been I have gotten fed up with emacs modes that are good and a lot of effort to write but just end up adding a lot of stuff on top that make it difficult to customize or customize the the standard way and returning to simple lists could be good.
That’s why you got org files and a handful of lisp functions to turn them into a living documents. Using lists take that aspect away while markdown is just not that good to serve such a role.