[scanr]

Java 8 looks good enough to make Java a reasonable candidate for Java.Next. Especially given that there doesn't appear to be a clear winner between the alternatives (Scala, Groovy, Clojure, Kotlin etc.).

Java 8 seems to have borrowed a lot from Guava (Optional, Function, Predicate, Supplier etc.).

Extension methods as well as default methods on interfaces would have been nice.

[swift]

Mixins would be great too.

[tomjen3]

Default methods in interfaces makes them mixins.

[notimetorelax]

Or something similar to Clojure protocols.