This could rapidly turn into a PyPA governance question, but in my view, the current answer to that question is “projects make their own choices”. Pip chooses to defer to packaging because that’s easier for us.
This does mean that adoption of new standards that have the potential to involve a significant impact happens slowly, and in irregular bursts. Maybe that’s something the new packaging project manager might have a view on - I’m not sure what that role involves.
As someone wearing both hats, I would like packaging to drop support. And then, in whatever pip release happens after that, pip would drop support.
I imagine we’ll get a barrage of users going “why you break me” around the time pip makes the change, so we’d likely want to do some sort of expectation/change management for that.
This (the general problem of managing the impact of breaking changes caused by adopting new standards) is definitely something I’d like to see the new packaging project manager get involved in. Does anyone have an idea of what the scope of the role is and how we could start a discussion like that? (As far as I know, the role was only filled a day or two ago, so I don’t expect anything immediate here 
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