I personally like the way that Obsidian and Typora hide the styling: when you get to where it would be, it shows up on screen to show you it's there causing the styling. When your typing indicator moves away from it, it hides it. Some don't like it because it can cause some displacement of text a bit because it's now showing characters it didn't before.
I found Obsidian’s way of doing it to be a bit jarring at first but now that I’ve used it for awhile I personally quite like it. Just takes a little while of getting used to
You could probably do this in a way that doesn't trigger text reflow if a popover appeared with the visible syntax exactly positioned such that the extra syntax slightly obscured surrounding text. It's a tradeoff but I think that might be slicker.
Not a user of either of those but that sounds an awful lot like "Reveal Codes" from WordPerfect which saved my ass more than once when formatting got screwed up in a document.
