Earlier quoted context omitted.
PHP has a rather strict no-BC-break policy for minor releases. As such the 5.x series improves the language mostly through additions. I think that's good. PHP has been missing a number of things that are now present. However that doesn't work forever, at some point you need to clean up some of the old stuff. That's why a PHP 6 release is planned in the near future (i.e. somewhere in the next three years ^^).
The very first programming book I bought was "PHP6 and MySQL5" by Larry Ullman. I bought that one specifically because I had another job (career, really) and I knew it was going to take a while before I really got into programming and I didn't want to buy a book that was going to be out of date in 2 years. That book is now 6 years old, out of date, and PHP6 is still not released. Maybe 6 is just an unlucky number wit…
However due to problems and internal conflicts the effort was stopped a few years ago and there has been no progress since.
If this goal hadn't been stated PHP 5.3+5.4 would probably have been PHP 6 (they have some major new features). Core API cleanup never has been (and it doesn't look like it will soon be) a goal for a future release, unfortunately.