September 2018 - Flutter release preview 2 released (can't find the date on RP1)
December 2018 - 1.0 release of flutter
Flutter is not going to be the primary framework over JVM-based for Android any time soon, these things takes lots of time. But android didn't pick Kotlin over flutter, it was just not ready to be the preferred language at that point in time. I would even say Kotlin could have been promoted even sooner then it was
September 2018 - Flutter release preview 2 released (can't find the date on RP1)
December 2018 - 1.0 release of flutter
Flutter is not going to be the primary framework over JVM-based for Android any time soon, these things takes lots of time. But android didn't pick Kotlin over flutter, it was just not ready to be the preferred language at that point in time. I would even say Kotlin could have been promoted even sooner then it was