I recommend against this.

Any additional specialization code will necessarily slow down other cases handled by PyObject_GetItem.  So, the merits of speeding-up tuple indexing need to be weighed against the costs (slowing down other code and the excess loading of ceval.c with specialization code).

Also, I reject the premise that there is no conceptual difference between list and tuple indexing.  The former is a primary use case for lists and the latter is only incidental to tuple use cases (see the endless discussions on python-dev and comp.lang.python about why tuples are not to be regarded as immutable lists and in fact have a different intended set of uses).