I’ve worked for 2 companies so far which maintain a bit of Android code and neither used Kotlin. GitHub search for “#android language:Java” reports 49K repositories, while “#android language:kotlin” reports 25K repositories. GitHub is biased towards greenfield projects, not legacy corporate codebases, so I’d expect the ratio of Java to Kotlin code in non-open-source software to be much higher. I wouldn’t be surprised if it’s more than 10 times higher.