PHP should do a real major compatibility break and remove $ sigil from variable names. It's gonna be worth the pain!
Such a change makes it a completely different language with no compatibility. Thus all previous code is lost, no easy migration paths (especially for libraries which would like to support both during transition)
Maybe https://getrector.com could auto-fix 99% of code but it would still be very hard to get adoption.
What about introducing a new file extension for this? Something like MyClass.p so that .php is for classic syntax and .p Can support newer syntax? You could support old codebases while at the same time support better syntax.
It’s probably too much for the core php team to maintain both though