The current state of the PR doesn't hinge on the pure Python implementation, we went with a very simple tuple subclass to keep the two more closely in sync and because we don't need any of the additional functionality that namedtuple brings, but if it were any more complicated than what we did we probably would have just gone with a namedtuple.

The only thing that's holding things up now is that we're working out a way to maintain the ability to pickle the object without making the class public. This is not really a hard requirement, but I'd like to give it an honest effort before calling it a day and just relying on "it's not in __all__, therefore it's not public." (I should note that we can only take that approach after issue #38155 is resolved, which is another reason for the delay).

In any case, the bulk of the conversation on the implementation has been taking place on GH-15633, sorry for the split discussion location, folks.