First things first
Elastic's upcoming IPO could be a much bigger deal than people expect, especially as a bellwether for the rest of the open source big data market that has sprung up in the past decade or so.
Hortonworks, Cloudera and MongoDB were obvious choices for companies to go public (even if their quarterly losses spook investors), because they were high-profile, had raised so much money and, in the case of MongoDB, attracted so many users. But Elastic is in a second tier of companies, which is exemplified by popular open source technologies, seemingly respectable businesses and relatively little fanfare. Elasticsearch, its flagship technology is nearly ubiquitous and being used for things well beyond standard search, but somehow Elastic isn't often mentioned in the same breath as other "unicorns" of enterprise IT.
Other companies in the same vein might include DataStax, Couchbase, Neo4j and MapR. All companies that have been around for a while and have grown large enough that the only real exits might look like an IPO, a pricey acquisition or, perhaps, something much uglier should funding dry up. With Hortonworks, Cloudera and MongoDB out and surviving as public companies, maybe their open source peers are gaining the confidence to step up and put their business models -- the good, the bad and the ugly -- into the public eye.
Given its wide adoption, Elastic is probably in as good a position as anybody to test the waters. For more on the company's evolution, starting Elasticsearch's roots as a hobbyist search engine for recipes, check out my podcast interview with founder and CEO Shay Banon from last year.