The decision to only support Unicode 3.2 is simply because the StringPrep framework [1] (which XMPP's nodeprep and various other protocols use) is forever tied to that version of Unicode.

Current work is on the PRECIS framework [2] which uses the metadata for Unicode code points to determine how to handle them during canonicalization instead of relying on a hard coded set of mapping tables. There's still a lot of work to be done, mainly to review that the process works reliably and doesn't introduce subtle new issues. Peter Saint-Andre (one of the authors of PRECIS) has just started on a Python tool for testing how a given version of Unicode is handled by PRECIS (https://github.com/stpeter/PrecisMaker).

[1] https://www.ietf.org/rfc/rfc3454.txt

[2] https://tools.ietf.org/html/draft-ietf-precis-framework-08