I guess he cares (he spent the time expressing it in writing) and I care (I took the time to respond) :)

Also I'm not considering alternatives just because Java 9 broke stuff. There are lots of other reasons why Java irritates me but I felt it was still a winner when you balance up all the factors. But if backward compatibility is no longer going to be prioritised, then this shifts the calculation so that it's at least worth it, in my mind, to evaluate alternatives. So we're going to try Kotlin on a fairly small self-contained project.