> or me, the differences between MRI and other implementations effectively make them different languages, I'd jump to Elixir before giving JRuby a shot

Wha? Sorry but this sounds pretty FUDdish. I have never had an issue with JRuby to the extent that you are describing. Do you have some examples?

I know of many large app deployments in JRuby at large household name companies.

The only thing JRuby doesnt have is the relatively niche CExt functions.