Operator overloading (again) and functions
Add operator overloading to Java but make it only usable within the java.* and javax.* package hierarchies. This would allow complex, interval arithmetic, matrix and vectors, etc. to be added. It would allow JCP JSRs to add well thought out operators while not allowing the abuse that making the facility available to everyone would lead to.
Add a "function" keyword modifier to methods that means that the method has no side effects. This has most of the advantages of "const" modifiers to methods and their parameters while being very simple.