There is a way to do it: https://en.wikipedia.org/wiki/Variation_Selectors_(Unicode_b...

However, it's not used widely and has problems with variant-naïve fonts.

Yeah. I would have favored something like introducing new codepoints with "automatic fallbacks" if the font doesn't support that codepoint, to ensure backward compatibility. There would be a one-time hardcoded mapping table introduced that font renderers would have to adopt.