I agree that this probably isn't right for core Python.  But I think this 
is valuable work, and it would be nice to see this patch available and 
maintained somewhere, if anyone has the energy.

I'm wondering whether the Sage folks would be interested in this;  as I 
understand it, they currently have Python integers *and* Sage integers 
(based on GMP), along with various rules about which integers you can use 
for what.  For example, according to

http://www.sagemath.org/doc/prog/node21.html

you can't use a Sage integer as a list index.  Having just one type of 
integer might simplify things a little.