This is an interesting architecture, but on at least two of the three target platforms, specifically Android and web, I think it would be better to use Kotlin Multiplatform [1] than Rust. Because Kotlin compiles to JVM bytecode (and ultimately to Dalvik bytecode) on Android and can compile to JS for the web platform, it means that for both of those platforms, the whole application can be compiled and linked together in a single type of object code, leading to lower overhead and a smaller bundle. There's also no need for serialization and deserialization when going between cross-platform and native code, further reducing bundle size; deserialization in particular requires heavy glue code.

But I don't yet have any experience with Kotlin Multiplatform, especially Kotlin Native for iOS. Does anyone know whether Rust has any particular advantages over Kotlin for any of the three target platforms?

[1]: https://kotlinlang.org/docs/multiplatform.html