Functions/Methods as first class objects
I want to see Java be the first (i think) mainstream programming language to treat functions as first class objects. I think now that java 5 supports dynamic instrumentation this will be possible (easy?) to implement, this in a type safe manner, in Mustang.
If we had this feature we would be able to express general concepts/ideas as procedures. This would also clean up a lot of the event handler code that we are so used to. Instead of having to pass a whole object as a listener, when what we really want is to have a function run as events are generated, we just pass in the function.