Search results could be delivered to the user more quickly if instead of blocking on the HTTP request to ElasticSearch, we make the request asynchronous, and proceed to do whatever work is still pending and not contingent on the response (such as building the user interface).
Because Elastica is an extension, and because it supports pluggable ElasticSearch middleware, it is a viable place in our stack to experiment with Hack. The impact could be substantial.
See http://docs.hhvm.com/manual/en/function.hack.curl-multi-await.php