The thing is, letting the user format some text as bold isn't really enough for many use cases. You need custom block and inline elements, such as tables, highlighted code or formulas.
It won't be simple or easy, but this sounds like a solvable technical problem. Its solvable today if you're willing to use hacky javascript.
Inline blocks should probably be embedded DOM nodes or something - just like contentEditable does today. Then they can be themed & styled like everything else - using CSS.
There's some complex UX patterns to manage - like deciding what should happen if the user hits backspace when their cursor is right after an inline block element. If the user uses the keyboard to move the cursor "past" an inline block element, should the cursor enter the element or skip it?
This sounds like exactly the sort of problem that the web standards committee is designed for.
Inline blocks should probably be embedded DOM nodes or something - just like contentEditable does today. Then they can be themed & styled like everything else - using CSS.
There's some complex UX patterns to manage - like deciding what should happen if the user hits backspace when their cursor is right after an inline block element. If the user uses the keyboard to move the cursor "past" an inline block element, should the cursor enter the element or skip it?
This sounds like exactly the sort of problem that the web standards committee is designed for.