Perhaps Kotlin/Native could be made to map to some common subset of GObject and COM? Then it would interop with commonly used object models on both Unix and Windows. (The systems are at least conceptually similar, but I don't know if they differ too much in the details to make it workable.)

tunedal: not sure if either COM or GObject are native object model on platforms where Kotlin/Native is aiming to (iOS, IoT, embedded), and also object-level interoperability imposes too many limitations on runtime, so maybe primitives + strings are better things to go over the language barrier

I guess GObject is mostly useful with GTK and GNOME, but COM is the basis for UWP, so it would be useful on Windows-based phones and tablets (although I'm mainly interested in the old-fashioned desktop variant). C# provides COM interop not as part of the core language (like VB6 did) but through a bunch of attributes that specify how to convert the data types and things like that – couldn't Kotlin/Native do that with annotations? https://msdn.microsoft.com/en-us/library/aa645736(v=vs.71).aspx https://msdn.microsoft.com/en-us/library/system.runtime.interopservices.marshalasattribute(v=vs.110).aspx