This also means Mastodon uses now three databases to run (Redis, PostgreSQL, and ElasticSearch), and I don't understand why people don't think this is a problem. I suspect they are conditioned to just agree with Gargron. ElasticSearch being optional does nothing to change anything, because you will lose a piece of functionality that most people find useful if you don't use it.
A piece of functionality, may I add, gargron wasn't originally going to implement!