Is this a real cause for concern? Simply don't copy code with strange unicode charecters, just like you don't copy code with blocks of bytecode.
At the same time, one can't just put a blanket ban on Unicode. It exists for a reason. People want to use their native languages to name identifiers, or at least to write comments. Restricting ourselves to ASCII again and thus forcing English on everybody is not a solution.
Yet most programming languages force them to use English Arabic numbers.
Wouldn’t it be great to use Roman numerals?
And then images in source code are really difficult to handle. Wouldn’t it be nice to compile a word document with embedded images?
I think I wouldn’t mind staying with ASCII for source code, except for string literals (difficult enough).
What I have in mind actually exists already: Jupyther notebooks, which combine code, text, and resources combined into a nice JSON ball. Horrible for SCMs and editors without using special plugins of course.