We are still using ES 1.7.5. We have an on-premises product used by let's just say more than a hundred, less than 10,000 customers.
We were hoping to move our customers to a more current version of ES, but unfortunately, have fields with dots in the name. We are now working on migrating our customers' indexes and moving to a more recent version, but I am dismayed by the wholesale removal of features such as types and parent-child queries that were fundamental to our initial adoption of the product.
We will probably initially target version 5.6 because, aside from the dots, it is reasonably compatible.
Do you foresee a time when Elasticsearch's programmatic interface and feature set become more stable?