Copyleft-next should not do unilateral disarmament via the sunset clause

[Josh Triplett]

I can very much appreciate arguments that copyright should not last as
long as it does.

However, as long as proprietary software continues to have the full
duration of copyright at its disposal, it seems like a license
purporting to be the future of copyleft should not be unilaterally
disarming by turning into a permissive license after 15 years.

The world already has enough permissive licenses, and far too much
pressure towards permissive licensing and away from copyleft. I don't
think an intended-as-flagship copyleft license should be adding to the
steady decline of copyleft towards permissive licensing; that seems like
a step backwards, and a good reason to continue using the GPL instead.

In general, the concept of doing better than the GPL seems like a good
idea. However, introducing regressions relative to the GPL runs counter
to that goal. There's already going to be a substantial amount of
bifurcation between this license and the GPL; it'd be easier to argue
against that bifurcation if this license were an improvement over the
GPL in every respect, including in the strength of its copyleft.

- Josh Triplett