What would be nice would be something that goes both ways - both promotion and demotion. One implementation detail would need sorting out:
For some documents I go to Heading Level 5 before heading into bullets. md2pptx ascribes meaning up to 4 (3 being w content slide and 4 a card within a slide). Most people want to go to 3, I expect.
So some way of saying e.g. “the highest heading number is n and after that it’s bullets” would be handy.
A nit is that I use asterisks rather than dashes for bullets as dashes can be used by Taskpaper.
Shame I’ve got too much in to build this myself right now.