I am excited about the changes in PHP 6 previewed in PHP 5.3+. However, I wonder why it takes so long to release PHP 6? Books about it have been published since 2008, and announcements on it since 2007, but I am yet to hear about an alpha or a beta. Why does it take so long to release it? Or is that the way it goes with all languages when they transition to a major release where I guess it takes around 4-5 years to release?
The release timetable is not unusual for languages, and it's not even that unusual for PHP: 5.0 was released in 2004, but 4.0 was released in 2000.
Compare this to the last stable releases for C (2000), Fortran (2003), or C++ (2003).
One other thing to keep in mind is that 5.3 was a major release in all but name. It adds a lot of stuff that was originally destined for PHP 6. Due to development problems with unicode support (a major part of PHP 6), it was decided to release what was stable at the time as a 5.x branch.
PHP6 Is not something that is really aimed for right now. Originally it was going to be the "namespace/closure/plus some" release. With the release of PHP 5.3 containing most of the cool stuff that was supposed to be in PHP 6, its not really known what the current trunk will be versioned. Its said it "PHP 5.4, PHP 6 or maybe even PHP 7."
Either way the functionality is looking awesome. Things like array dereferencing (example:
echo foo()) are already in trunk for everyone to play with. I wouldn't put too much concern on how long the '6' release is taking. 5.3 was released in July of 2009 (which contained most of the functionality that was supposed to be in 6) and they recently released 5.3.3 (July 2010), so it still seems like development is running smoothly.
I don't think there's any demand for PHP 6. I mean, what do you expect 6 to have that doesn't already exist? True unicode support is all I can think of, and that doesn't even impact me at the moment.
Also there's been new features added recently, like namespaces and the phar packaging system that need some time to soak in. You don't want to throw even more features at the community before they've adopted the old features.
Finally the industry as a whole has been slow to adopt new versions of PHP. There are still applications being written that target 4.3. The industry and community need to catch up before PHP goes much further.
Join the mailing lists
If you join the PHP internals mailing list you can know exactly what is happening. You will see people talking about certain patches, optimizations and some new features. Occasionally they'll discuss about the next release, but it is somewhat ethereal right now.
You can also learn more about what is happening by watching the PHP RFC wiki page. Some months ago they were pushing for a new release that had traits (which is already accepted and mostly implemented and refined AFAIK) with it but they decided to wait, don't exactly remember why, but unicode is one of the factors that is stalling the new release.
So long story short, there is no date, but you can ask in the mailing list yourself and you'll get a better and more accurate answer. I've seen no recent talk on the next release.