I've done two large search projects in the last year. One with Postgres search and one with elastic search. The elastic search version was trivial to configure, and was embarrassingly superior to the point where I wish I had never considered Postgres.
For many the source of truth is still Postgres, but you may want some of the flexibility and search power that comes along with ElasticSearch in many cases. An interesting project to look at may be ZomboDB which lets you maintain ElasticSearch indexes from directly within Postgres and query from within PG directly. (https://github.com/zombodb/zombodb)