1.3.20 is going to support Kotlin DSL in multiplatform projects. You can get an idea how it would look like from the test data projects, for example from this one https://github.com/JetBrains/kotlin/blob/master/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-lib-and-app/sample-app-gradle-kotlin-dsl/build.gradle.kts