One difference is that there won't be a built-in string type with operator[] defined as something other than returning the byte at the indexed position in the array of bytes. There could be most other things one would expect from language-level string support though.

i don't think so. the answer is presumed no, because everyone in the relevant thread including language authors and stdlib authors (with plenty of overlap) agree that it is not, and agree there are functional distinctions about what is possible on either side of that dividing line (mostly due to zig not supporting custom operators).