PS: Is it not simply oversight that the Update spec does not support the insertion of namespace nodes, although XQuery 3.0 does define their constructors? Would a feature request have any chance?
If I remember correctly, the namespace constructor had not yet been defined when XQuery Update 1.0 was finalized. On XQUF 3.0, not too much time was spent, so it can indeed be regarded as an oversight.
While it may not be too much effort to implement, it could take some time to specify it properly. Anything involving namespaces takes much longer than it seems at first glance…