If you're using parentheses, as has been recommended for decades, there is no problem. Otherwise, it is likely that such a change would adversely impact previously working code. There just isn't a pressing need to change it.
It seems to me that C would benefit greatly to iron over its many inconsistencies and exactly the kind of thing people expect in new revisions of the language.
Also, I dont see how it would impact previous working code when compilers already do things like allow selections between versions of languages a la C99, C2x, etc. Users could just avoid the new version if they don't feel like changing.
But, I do see the benefit of having a language "frozen in time" which never really changes and can be mastered painlessly without having to refresh on new versions. Perhaps C is special/sacred in this regard.