It's a limitation per iOS project, not per gradle module. That limitation has been relaxed some in 1.3.70, but I haven't had a chance to try it out yet.
Previously the limitation existed because there could only be one version of Kotlin in the entire app. Now you can have multiple frameworks but they're each their own "world" as far as Kotlin is concerned, so Kotlin types that exist in both frameworks resolve as different types in Obj-C/Swift.