Hi!
I'm at WikiConference NA today, and I was chatting with someone from OCLC https://en.wikipedia.org/wiki/OCLC, and he mentioned that BlazeGraph can be configured to call out to a full-text search engine. It looks like it only works with SOLR out of the box, but the documentation https://wiki.blazegraph.com/wiki/index.php/ExternalFullTextSearch mentions that Elasticsearch is a candidate search endpoint.
Technically it is possible, and I looked into it, but given that we have a gateway to Mediawiki API (which can do the same search, essentially) I decided not to pursue this for now. We'd have basically to duplicate the work we've done in Mediawiki to compose proper Elastic queries, parse results, etc. and the best we'd have is the same thing we already have with Mediawiki API search. So I decided not to duplicate efforts for now.