DomXPath extension

Hey guys, I've been working with the DomXPath class and would like to use the full XPath vocabulary for searches. But before I go trying to write an extension that does this I'm just wondering what the current status is and when you all think everything is going to be supported. I'm mostly interested in making XPath functions work (e.g. count()). But no sense in re-inventing the wheel if someone else is already hard at work doing this!