What about a sort of "working group handfasting"?
Much lower bar for chartering, but the initial goal of the group is
very short term (like 6 months) and mainly designed to see if the
group seems likely to be productive. With the expectation that,
by default, such a group would end after the initial period, unless
the group's members actively think it should continue; it would
take positive action to request a recharter at this point, with a
longer term mission, but it would be expected that such a recharter
be approved if the consensus of the group is behind it.
That seems similar to the idea of a higher bar for chartering, because
it makes the bar be "actually try having a working group for a number
of months and see what comes of it" - much like Dave's suggestion.
But, it also makes it much clearer and more transparent what is going
on, easier for new people to see it, and gives some support and
guidance to reaching that higher bar, making it more likely that
worthwhile efforts will clear the bar.
-- Cos