[TODO] Retro and cleanup

[isaacs]

Several RFCs are sitting in the "accepted" folder, but actually are not slated for implementation, changed implementation, or just no longer make sense.

Let's go through all of those and identify which accepted RFCs to move to the implemented folder, which should be removed/updated, and which should be left where they are. We need to identify a good process for removal. Eg, does it take a new ratified RFC? or can we just agree to un-ratify something? I'd prefer it not be too much make-work, but also don't want to make it seem like we're not making good on a commitment, as that reduces our credibility when we do ratify RFCs.

As part of the same process, we can revisit some very old PRs that aren't going to happen for whatever reason, and close those out as well.