What does PyPy have to offer over CPython, Jython, and IronPython?

Question

From what I have seen and read on blogs, PyPy is a very ambitious project. What are some advantages it will bring to the table over its siblings (CPython, Jython, and IronPython

Answer 1

In case that Python gets a real JIT I think it's going to be as fast as any other implementation.

The advantage is that it's much easier to implement new features. One can see this today by observing the library. Often modules are written in Python first and then translated into C.