Lunr and elasticlunr are awesome projects. I was part of a search team and we were banging our heads against the wall trying to figure a way to serve a new feature request (basically some advanced autocomplete functionality) in a way that fit in with what we were currently maintaining.

It took me literally half an hour to implement this using elasticlunr on the browser. We will went with the backend solution as it felt more extendable, but this got me thinking there's some abuse of ES for things you could easily do that way.