What ever happened to XPathReader
XNode.ReadFrom combines the power (and supported status) of Linq to XML with the ability to process a stream rather than loading the entire file into memory
http://msdn.microsoft.com/en-us/library/system.xml.linq.xnode.readfrom.aspx
I suspect that LINQ-to-XML happened. However, the Mvp.Xml project on CodePlex has many features that relate to this. You might want to take a look at the XPointer.NET library they have developed and the XPointerReader.
Also, you might want to take a look at this FastXPathReader on CodeProject (I don't know how effective it is).
As for XPathReader, all I could find were the links you provided and links associated with those. It looks like it disappeared. Like I said, I think LINQ-to-XML was the outcome, but I'm just guessing.