I was able to get this working in just a few short hours the other day thanks to VIAF's well-documented APIs. Like geonames, the EADitor user can still select arbitrary terms from local authority lists or input new names, but searching VIAF will go a long way toward tightening controlled access terms in EAD finding aids. Moreover, it will enable direct linking to various services from the finding aid display page itself, and those services often provide external links to other useful sites, like wikipedia or worldcat.
The links to terms listed above point the user to EADitor's search results page for that particular query. The image to the right of the term links the user to the URI for that term, hosted by the appropriate service, e.g., http://www.geonames.org/4811020/ for Kirby (W.Va.) or http://viaf.org/viaf/126085739/ for the American Numismatic Society. Also of note here is another significant change. The results from geonames are transformed into AACR2-compliant place names, with the exception of Malaysia since I have not yet been able to find a list of standard abbreviations for its territories.
I see also another use for controlled vocabulary service integration. Third parties will be able to query the EAD collection for finding aids which contain particular terms. For example, suppose that from the VIAF record for Thomas Jefferson (http://viaf.org/viaf/41866059/) one can link back to an institution's search results page for finding aids containing @authfilenumber '41866059' from @source 'viaf'.
After all, better metadata is the foundation for better information systems.
NOTE the code is available below: