Yeah, I’m right there with you on letting the clients control what they see (and being able to fall back to plain-text). My design is basically a replacement for markdown with extra horsepower thrown in. I’m making a lexicon for it, but the idea is that it works primarily as a portable, stand-alone format. You can check out the intro page here: https://neodoc.style/
(I’m also writing a post to start a thread to discuss it. I should have that posted sometime tonight.)