So why does PunBB still support PHP4, a discontinued product?
Because we can. We don't use any PHP 5 only features, so there's no reason to drop support.
One of the devs answered that "PunBB does not require any features of PHP5." But what about the future of PunBB?
When we want/need those features, we can raise the version requirement. There's no reason to arbitrarily raise the version required. We have no problem doing so when necessary (eg: PunBB 1.3 requires at least PHP 4.3, which is a higher requirement than 1.2, and also requires a newer version of MySQL).
There are many great new classes and functions that come with PHP5, like filter_* and PDO.
"This vulnerability is also one of the reasons why we do not recommend using ext/filter for user input filtering/validation. Whenever there is a fault in the code the application might be open for attacks and only the admin of the server is able to fix this. This is especially bad in shared hosting environments."
We have our own DB layer set up, I don't see why we need another abstraction layer.
SimpleXMLElement and XMLWriter will allow you to easily parse extension info and syndicate feeds.
Seems to me like we're already doing fine parsing extension info, and that code could be used to syndicate feeds as well (I think). What's the problem?
And SPL will be great once (if) PunBB becomes OO.
Super. But it isn't. So it's irrelevant
There is absolutely no reason to not discontinue PHP4 support, and move on to PHP5.
Except for the fact that we neither want nor need the features given to us only in PHP5. We don't want to stop support for the sake of stopping support. If there are compelling reasons (like there were in 1.3), then we raise the version number.