Yes, I write SpringBoot microservices and IntelliJ plugins using Kotlin. Any new code is Kotlin, but there is still a ton of Java, which I don't consider "legacy", since it works, and if I can sanely add Kotlin when necessary, I don't see the need for "full rewrite".
You may get more traction by asking the Kotlin community
Just make sure to test the regex instead of blindly slapping it in assuming it works ๐