> Saying "once Java has caught up" ignores that Kotlin, at that point in time, will be even further ahead of Java most likely.
This assumes that there is much "ahead" to get and that people want more features (well, some do, but the vast majority don't seem to). If the "catching up" terminology applies at all, it certainly doesn't mean feature parity with every other language. That's like a compulsive hoarder seeing a neighbour buying a lawn-chair and saying, "nice to see you finally catching up!" Once you've "caught up" with the expectations of the majority of programmers, there's not much more catching up to do. Neither Scala nor Kotlin have broken past 5% share of the Java platform, even when Java was behind mainstream expectations.
So sure, there will always be some small percentage who like more features than the mainstream fashion, but it's been clearly shown that you can't appeal to that minority and to the mainstream majority at once. Java (the language) tries to appeal to the latter, not the former.