PHP 5.1 is just around the corner (at least RC 1) and some new, but not really groundbreaking XML features come with it (see my ApacheCon slides for more information).
Personally for me, the XML support in PHP 5 is quite feature complete and I don’t have any pending TODOs for it. But maybe you have some ideas, what could be improved or what could be newly implemented. This is your chance and I’m really interested in hearing from you. Just leave a comment below. Maybe me or someone else will find the time to actually implement it for PHP 5.x :)