Major PHP versions are the evolutionary jumps for the language. They don't tend to worry as much about backwards-compatibility when going from PHP3 to PHP4 to PHP5. I've read that PHP6 was supposed to take it further and outright remove a lot of deprecated and insecure aspects of the language, but I don't know if or when PHP6 will be released.
I agree that they should take things even further and really clean up the language before releasing the next major version. Fix the needle-haystack vs. haystack-needle inconsistencies, function naming conventions, and so forth.
The adoption rate of a new major version on shared hosting providers is relatively slow, so it'd be a perfect time to really shake things up and clean it up.
I would suggest that minor PHP versions often are, too. Significant internal changes between 5.x versions have caused some code to break (and other code to act very differently than it was originally intended to).
I agree that they should take things even further and really clean up the language before releasing the next major version. Fix the needle-haystack vs. haystack-needle inconsistencies, function naming conventions, and so forth.
The adoption rate of a new major version on shared hosting providers is relatively slow, so it'd be a perfect time to really shake things up and clean it up.