In clr land we've already seen c# adopting a fair few functional things - I think largely ahead of Java. There's this pretty interesting article from an f# (if anyone's unaware that's a Microsoft built functional language on the clr) tutorial site addressing reasons to still use f# over it. It's quite opinionated but worth a read and largely applies to Java/functional on the jvm: http://fsharpforfunandprofit.com/posts/is-your-language-unre...
They take a different view to the comparison, looking at things the language enforces more than features/syntax it permits. Of course backward compatibility and plain sanity stop Java making such enforcements so the argument is that the functional languages maintain some strong advantages.
There is a Haskell implementation for the JVM if you want a language like F# (it's called Frege).
Kotlin has some FP features. You can easily make immutable data classes (one line definitions of struct like things), you have map/filter/reduce/etc with a much more efficient approach than Java 8's streams framework, the compiler knows about tail recursion, there's some basic forms of pattern matching.
I suspect Kotlin will take a breather from new features for a while now to try and stabilise what they've got. But after that, I imagine a few more FP features might materialise.
Sorry, I think I was a bit unclear. I have no doubt the jvm can support a functional language - scala isn't bad and Kotlin looks really nice. My point is more that Java is constrained in how it can compete with functional jvm languages in much the same way c# is against functional clr ones. The linked article explains those limits a lot better than I could :)
They take a different view to the comparison, looking at things the language enforces more than features/syntax it permits. Of course backward compatibility and plain sanity stop Java making such enforcements so the argument is that the functional languages maintain some strong advantages.