I don't understand. No matter what fancy things you do with superscripts and subscripts, you're not going to be able to do even basic things you need for equations like use a fraction bar, or parentheses that grow in height to match the content inside them.

At a fundamental level, Unicode is for characters, not layout. Unicode may abuse the ZWJ for emoji, but it still ultimately results in a single emoji character, not a layout of characters. So I don't really understand what you're asking for.