Having an "official sandbox" is completely irrelevant (and probably counterproductive) if core development is happening in a DVCS. If people want to experiment, they will be able to experiment by branching into their own repository. Trying to create an "official sandbox" (or, more likely, use the existing sandbox) defeats the whole point of the exercise, since it just brings the CPython admins back into the loop and will generate a pile of irrelevant traffic on python-checkins.
In short, a moratorium that said "we won't accept things into trunk, but you can still pester us to add things to our official sandbox" would be a pointless exercise.
Moving to a DVCS, putting a core language change moratorium in place for a few years, then looking to see what improvements have been developed outside the core tree as the moratorium is running down (and what feedback has been received over that time) would be far more sensible.
100% in agreement. marcos