It would be extremely useful to see a mechanism like the following to allow further extensibility of XQuery:
to add a recent datapoint,
my recent impl of Adam Retter's RESTXQ for marklogic
required the usage of ML xdmp:functions and xdmp:annotation functions to get a list of functions in the current environment and what annotations a function may have.
having these functions exist would help promote a more language neutral solution
Assigning to future requirements per Working Group decision (https://lists.w3.org/Archives/Member/w3c-xsl-query/2012Oct/0087.html).