Java DSL

What's the raison d'être of creating a Java DSL and how much would this differ from the original Scala DSL?

What’s the raison d’être of creating a Java DSL

Adoption.

how much would this differ from the original Scala DSL?

It will be very similar.
See https://github.com/gatling/gatling/blob/main/gatling-bundle/src/main/java/computerdatabase/advanced/AdvancedSimulationStep05.java

I guess it's the "helper" methods that'll define the transition, and am I right in saying that the Gatling code base has increased it's Java constituent?

There may be some trepidation towards the Oracle JDK as other languages *could* be of interest, but it's probably not worth it and a correct decision to close the Kotlin open issue.