On the meta point, I agree with Simon's position here: we should avoid
giving unconditional acceptance to underspecified proposals, only to
potentially discover problems later. But where a proposal is not
precisely specified, it would be preferable to accept in principle (so
the author is not left wondering whether the idea has a chance) and then
ask and support the author to finish the spec before merging the PR.
I agree too. I was thinking about it over the weekend: we kind of need a status to say “we pretty much know we're going to accept it, so go ahead and do the implementation, but we're still working the details out together” (I was thinking in particular of the choice of string delimiters from this proposal: it makes no material difference to the implementation what we eventually settle on. So if there are questions, we should avoid holding the implementation effort back just because we're having a discussion about what we think it best).