Would it though? I’ve been thinking about this for a while.
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
Maybe https://getrector.com could auto-fix 99% of code but it would still be very hard to get adoption.