On Jul 17, 2018, at 5:27 AM, Paul Moore <p.f.moore@gmail.com> wrote:

There's also a PR cost, in that projects who have enthusiastically
adopted pyproject,toml as being a nice "common configuration"
location, will be left feeling that maybe that wasn't such a good
decision if it's causing them problems like this. Plus, projects like
towncrier will need to update their docs (yes, that's a bit ideal
world - the reality is that people simply keep doing what they do now,
and we get the message out via a gradual process of addressing bug
reports and providing the explanation there).

I think that this is the most important reason not to go too crazy here. We
should think of breaking changes as having a limited budget for introducing
breaking changes, and the question then becomes where do we want to spend our
budget? While something being relatively new means that the cost to our budget
is smaller, it still has a cost and I just don’t think this is a great place to
spend our budget at.

On top of that, I don’t think the end result is significantly or meaningfully
better for the end users, particularly if we ever get to a world where we
isolate everything by default (which would mean that we would have to have an
implicit requires of setuptools/wheel anyways).