This does bring up portability concerns and would cause further divergence of Read from the language standard. If not handled carefully, this drags us in an ever more implementation-defined rather than specification-defined direction.
As a data point for this discussion, a similar proposal to extend the Read syntax to add support BinaryLiterals was rejected over portability and silent behavioral change concerns.
Whatever we do here, we may well want to be consistent with how we treat both of these proposals.
If we do choose to accept this, we may well need to back and re-tackle #10092.
Currently, we do have at least one chink in the armor, in that Read is currently more liberal in what it will accept Unicode-wise than what the language specification states as a result of
I do think that whatever we do here, it should involve a conscious decision to either stick to the current report, or diverge from the current report and then to revise this part of the report.
If we can get the Haskell Prime folks to fix the language report to include them in the next language standard (if by default, even better!) then I'm fully +1. I'm also fully on board with both these and binary literals going into the language standard.
If we're doing this entirely on our own in the spirit of "being liberal in what you accept and conservative in what you output" then I'm personally far more dubious of the merits of that approach in practice, and will wait to weigh in from a CLC perspective until more feedback is in place.
-Edward