Last week Zend held a Q&A for the Zend Framework, which gave a good insight into the areas they're working on and the direction the framework is heading. Audio is now available (direct mp3 link) - there were a few technical issues (varying microphone levels etc.), but it's an interesting listen.
PHP version compatibility
One thing discussed was ZF's compatibility with previous versions of PHP. The framework is already a little unusual in that it requires PHP 5.x - most PHP frameworks work with PHP4, but this allows them to take advantage of the OO improvements that came with PHP5.
Backward compatibility has been both a blessing and a curse for PHP. The PHP team have done pretty well to ensure that for the most part, new releases of PHP don't break any existing scripts. I have plenty of scripts written back in the days of PHP3 that still work perfectly well.
For this reason, it's been easy for open source projects to ensure their scripts are compatible with older versions, and the majority list PHP 4.3 as their minimum requirement. Unfortunately this has greatly slowed the adoption of new PHP releases - hosts have few reasons to spend the time upgrading if existing scripts that work perfectly well don't use any of the new features.
There were some figures released recently about the adoption rate of PHP5, and they're really quite scary. 5.0 came out in July 2004, that's almost 4 years ago; but the majority of hosts (I think it was about 70%) are still running 4.x, which will no longer be supported after this summer.
It's a vicious circle that will only be broken if either the new PHP releases contain massive performance increases to tempt web hosts, or some amazing new features to tempt the big open source projects.
ZF's take on this was that they will continue to take advantage of features in new PHP releases where appropriate, but at the same time they can't just update their minimum version requirement whenever a new version of PHP is released, as vendors (Red Hat was given as an example) tend to lag behind the official releases somewhat.
In many ways it seems the development of the framework is driving updates to PHP itself. Some of the features upcoming in the next releases (PHP 5.3) such as namespaces and late static binding, have clear uses in the framework, and the team have said they will take advantage of these.
Also discussed was performance of the framework. I agree with the sentiment that hardware is cheap, developer time is not; and so spending ages trying to tweak the performance of an application before it becomes a problem can be a waste of time. This is certainly something I've been guiltly of in the past. However I'd also say that in general, performance of a framework should be more of a priority than with a typical web app, since any applications built on top of the framework can only be as fast as the framework itself.
The team are planning a performance review at some point in the future, and they'll be using the same tools developed for testing the performance of PHP itself, so it'll be interesting to see any tweaks made as a result.
Overall the team seem to be looking at the right areas and making the right decisions, and so the future of the framework is looking bright.