There are some very interresting issues about long type optimization:
faster long multiplication http://bugs.python.org/issue3944
Asymptotically faster divmod and str(long) http://bugs.python.org/issue3451
Use 30-bit digits instead of 15-bit digits for Python integers. http://bugs.python.org/issue4258 (mostly done)
But the issues are still open because the code is not easy to review and it's already difficult to benchmark (make sure that it's always faster!).
The project can be different than the 3 issues, it should be possible to find new ways to optimize operations on integers ;-)
There are other importants features to optimize like: - unicode string ("str" in python3) - I/O: io-c in py3k branch is already much better, but I'm sure that we can do better ;-) - etc.