[lifthrasiir]

Many languages (mostly functional) allow trailing apostrophes after alphanumeric identifiers, which mirror primes in mathematical and technical notations, so there are surely precedents.

Rust doesn't allow multi-letter character literals for the usual reason, so there is no real ambiguity. Some old editors do only have a very-limited syntax highlighter with fixed rules (e.g. no regexp), so such editors will be indeed unable to handle this, but they won't be able to support many other languages if that's the case.