If you are thinking of trying to develop an iOS app entirely in Kotlin, that's not something that will be supported (I don't think it will at least. That would require a high level of interop with obj-c or Swift).
I think a better, far less limiting approach that will be viable, and I hope to try, will be to create a shared library, that can be shared between an android and iOS project. Then the Android UI can be written in Java / Kotlin, and the iOS UI can be written in ObjC / Swift, and then they can interact with the shared kotlin library.