Could you ship emacs-nxml-mode in EPEL? If that's a prerequisite, I'm available to help with co-maintaining it there.
I've requested an EPEL branch: https://bugzilla.redhat.com/process_bug.cgi#c17
EL-4 tagged and built (37840). EL-5 tagged and built (37841). (How should I close this bug report?)
Adding FutureFeature keyword to RFE's.
Closing.