You raise an interesting point: Maybe Kotlin was the push Java core devs needed to increase their rate of innovation ("release cadence"). I saw similar with Netscape vs IE, Chrome vs IE, Clang vs GCC, Boost vs C++ foundation library, .NET vs Java, Java+.NET vs C++, Node vs Deno. Kotlin can continue to experiment with new and interesting language features. Those that prove most popular can be adopted by Java. Also, as a secondary effect, since Jetbrains wrote Kotlin and had the best IDE, they had a head-start to build the community. That also helped to sell more IDE licenses. (I have nothing against this 1980s spy movie "master plan": They are great company with many great products.)