ElasticSearch - Geolocation Search & Scale

I am the CTO for a startup in the GIS landscape, and I am thinking of Elasticsearch as the GEO Querying mechanism and it supports everything in GeoJson which is great. The question I have is I have a lot of experience with Elastic at scale, and its great, but how is Geo Search & Indexing at TB & PB Scale, and do you know of anyone using GEO Search at that scale.
I would greatly appreciate any insights here.

Thanks, Kartik