In that case, Kotlin makes even more sense especially with Kotlin Native, and Rust is unnecessary.

Kotlin is already multi-platform and can be re-used as the business logic in iOS apps with Swift as the UI and the Android app with a Kotlin UI (Jetpack Compose) or both iOS and Android apps can be written entirely in Kotlin.

That vastly reduces the maintenance and Kotlin is reused across all apps and keeps it at 2 languages at most.

No need to introduce Rust to achieve the same goal.