I agree that it would be great if they actually were fixing stuff instead of only adding stuff, but as someone who works in PHP on a daily basis, I certainly appreciate the addition of modern features as well.

It seems like one way for them to fix a lot of the old stuff while maintaining backwards compatibility would be to add new string and array (and dictionary?) classes with sensibly-defined interfaces. I imagine there are a fair number of less-obvious issues around that that make not as easy as that sounds, though.