I haven't had time for a while to do much work on this.  At the last posting this patch was basically done.  I'm sure it no longer applies cleanly.  The biggest obstacle to wrapping this issue up is the size of the patch.  It's hard to get a thorough review because someone would have to dedicate the time for it.  Furthermore, adding this much code introduces a debatable risk which needs to be minimized.

When I'm able to get back to this I'll likely split the patch up.  I'd really like to introduce some helpers (perhaps macros) to the C API for writing iterators, since the boilerplate involved is massive; just take a look at how much code in my implementation involves the boilerplate of creating iterators.  Unfortunately I don't know when my time will free up in the near future.  I still hope to land this for 3.5.