If Swift were practical to use for Android app development, I would absolutely do so. I enjoy writing Swift more than I do Kotlin by a good measure and not having to wrestle with gradle and proguard would be a nice bonus.
This would happen in about five minutes if a SwiftUI port was included.
Which ironically would be just like Flutter, totally bypassing any native UI.
My gut feeling is both teams probably have a plan for steamrollering the other in the event of anti monopoly measures forcing each to accept the other store. I.e. it is conceivable you could launch the Play Store on iOS and run a significant proportion of Android apps through a compat layer.
Except contrary to iOS, on Android the C and C++ surface is very small, and calling JNI is a huge performance bottleneck.
Anyone that cares about performance on Android has to write the userspace logic directly in Java or Kotlin, and use Android IPC instead of JNI.
Outside of Apple's ecosystem, is anyone using Swift?
Kotlin is growing in all areas, especially backend (being fully embraced by Spring/Spring Boot et al).
Kotlin-Java interoperability is at a completely different level.