Surely there are enough unicode code points for this not be a problem? Can you use the historical character + combining mark (which shows which 'newer' version

Surely there are enough unicode code points for this not be a problem? Can you use the historical character + combining mark (which shows which 'newer' version of the character to use), where the combining mark is ignored if the computer doesn't understand it, and only then it falls back onto guesswork/lang attributes. I don't know if that's a decent solution, but just guesswork doesn't sound like a good idea, because there are bound to be edge cases where it wouldn't work, and then we're back where we started...