There are, of course, a number of existing faceted search solutions that don't require any patches:
- The Semantic Drilldown extension
- The Special:RunQuery page of Semantic Forms
- The "filtered" result format in Semantic Result Formats (I'm assuming it still works, though I don't know)
- The SolrStore extension (again, I assume it works)
- Miga (http://migadv.com
) - not a MediaWiki extension, but can be used to provide a faceted search interface for SMW data
My guess is that you have some specific interface requirement, like that it should look like Exhibit, but I don't know.