New code in Collect has been written in Kotlin by default for a few years now (following this PR), and we've wanted to be able to write Kotlin in JavaRosa also.

It's important to note that adding Kotlin to JavaRosa means setting Kotlin up for Gradle and Maven as JavaRosa currently uses both. The former is for day to day to development and the latter is used to publish JavaRosa. It's likely that it's possible to publish using Gradle, so it could be that moving to this approach is easier than getting Kotlin working for Maven (and either is acceptable).

Existing code and test will need to converted to Kotlin to demonstrate that the tooling is working correctly. I think converting everything in entities would be a good candidate as this code is not being touched a lot at the moment, is fairly isolated from the rest of the code base (we've even considered making it its own module) and makes use of things like Java Streams that would benefit from conversion to Kotlin (EntityFormFinalizationProcessor for example).