The goal is to correct early design mistakes. It's also to reduce cognitive load on newbies. It is not a total rewrite like Perl 6.
I'm not going to cover the details because I think everyone should just read his slides whenever they come out.
Personally, I'm excited about the str vs. unicode unification as well as the stackable I/O library (a la Java). Finally, the csv module will no longer require explicit encoding and decoding.
Also, Guido is adding a "nonlocal" keyword to fix the scoping problem I've mentioned before.