The reason why Clojure is easy to teach on the job is that Clojure code base is small and code are very localized.
It's impossible to be productive in a large Java code base within a month even if you joined as a seasoned Java developer. But it is routine for a programmer who has not even heard of Clojure before to become productive in a production Clojure code base in two weeks. We do this all the time with our interns.
I work in Big Data at a Fortune 10 company. We don't even do what you suggest. There is very little appetite for niche languages that are difficult to just hire for. For example, we have a ton of Scala code due to a misguided belief that Spark must use Scala because it was written in Scala. We can't even go to the market and find people who have used Scala before. It's all Java developers, and many (most?) are not very good developers. So then I say we need to train organically if we want to have good Scala (and Java) people in the organization. Oh man! You would think I took away their birthdays! Train people? Dear god, no!
It's all optics and bullshit. Scala is pretty easy to pick up, as is any programming language. The problem is you have to spend the time. Time for most people, me included, is extremely limited.
In some parallel universe, I'm sure Clojure is the #1 JVM language. It's great and Rich taught me so much about functional programming and many other things. But at the end of the day, Clojure here in this universe didn't take off and I'm not sacrificing my career to beat that drum anymore. I tried hard, I really did: 2013 & 2014 were the years that were make or break. The wave didn't crest. When the people maintaining the plugins to Eclipse faltered, it broke down hard. IDEA never had solid support, either. Then, when the support tooling faltered, it was really hard to make the case to management, especially when other asshole developers were arguing for their pet tools. Type safety, meh! I don't need it, never have... So I write Java Streams and it pisses me off every single fucking day.
There is nothing more to say than "if you can find a job doing Clojure you are extremely fortunate."
