Rewriting React Native with Kotlin would make a lot of sense. Kotlin compiles to Java bytecode, so you don't need to deal with JavaScript engines, serialization/deserialization, etc. Kotlin will compile to machine code, so it'll be supported with iOS with the same advantages. Kotlin performance is better than JavaScript. Kotlin has async constructions, etc. Kotlin could be compiled to JavaScript for web apps, so code reuse will work.

The only thing that Kotlin misses is XML Tags inside the language, but they could be modeled with DSL API.

That said, I don't think that Facebook would rewrite react native. It's an impossible task and they don't really need it. But I hope that some big player will replicate react native with Kotlin.