I played with WebDAV implementation where the requests are XML parsed in JS and made it working on linux but got into 'too much recursion' on actual boards (available here https://github.com/opichals/refresh/tree/testing). Also UPnP mostly exposes XML stuff.
I think a non-recursive implementation of XML parse/serialization (into JS objects and back) might be an interesting feature. IMO there is no need to any XML tailored DOM implementation, plain JS objects should suffice.
Some exclude/include filtering in the parse method may be handy so that it is possible to just grab part of the XML content somehow and not eat all the available memory.