What makes sense to share is complex libraries, and usually I have been doing that with C/C++/Rust libraries. But it means that the team now deals with Kotlin, Swift and one (or more) of those "sharing" languages.
What I believe KMP and Swift for Android bring is that teams will be able to share libraries in Kotlin/Swift, so that they can keep writing in their preferred language without having to introduce C/C++/Rust.
I believe this approach is vastly superior to any kind of framework that tries to share the UI. Mobile devs, in my experience, want to use the native tools: Kotlin for Android and Swift for iOS.