Regarding the question of whether important users rely on dyadic grade: Yes they do, but typically in ONE cover-function - not littered throughout the code, so I don't think this would be a seriously breaking change.
IMHO dyadic grade is a nasty wart on the language, the functionality belongs in a library function (system function), not in a primitive. There are so many different ways to do "real" collation and it only supports a few of them.