I hope, every developer in Kotlin has to treat every object to be closed or immutable first and slowly let the mutability to creep in, as per the scope. An obvious shift in the mindset of developers can be achieved in Java or other language developers as well.
Kotlin has taken advantage of being immutable first and seems to have devised various concepts or features around it like "declaration site variance & annotations, type projection", it is not present in java, a java developer like me see it as a completely new concept. It requires a second level mind shift for developers, which my point of view is very difficult to achieve.
Features like value types,
pattern matching may / may not come to Java. Current Java developers don't have anything as such. We seem to have data classes in kotlin and pattern matching seems mostly not required with other features.
To my surprise, we have this page,
Comparison of Java and Kotlin. I just saw it only after posting the question in JavaRanch. It too does not highlight some features like "Destructuring Declarations", "Sealed Classes", "Type Safe Builders", etc., which look interesting and unfamiliar to Java developer.
Authors can point out such concepts/topics with some advise/suggestions. which could help developers like me to make trampoline jumps and emark on kotlin easily and to pay special attention to such concepts/features/topics.