I am happy to see the level of interest in this topic.
I don't know how much time commitment to expect from UW employees. I am
aware of employees from a few areas (computer science, libraries, the law
school, and communications) who have been involved in lightweight events
that relate to technology and public service. However, a multi-day
conference requires significant planning. If the WikiConference North
America user group and local Wikimedians are willing to put in most of the
time to plan the conference then I think that it would get moral support
from multiple UW employees, but I recommend not counting on UW to provide
free facilities or unpaid employee time.
I like Pharos' suggestion of first trying a Wikipedia Day one day event at
UW before making what would be a much larger commitment for WCNA.
Personally, I would be happy to attend an event in Vancouver BC, Seattle,
or Portland next year if my schedule allows.