Backcompat is important, but even better is using the new features Gradle 5.0 ships with, e.g. the production-ready Gradle Kotlin DSL 1.0 which you can convert to (from Apache Groovy) if you want code completion, error highlighting, and simple refactoring when you write your build DSL's.
See https://guides.gradle.org/migrating-build-logic-from-groovy-...