So there are numbers in there for calculating completion percentage over the last 5 releases before Train. Of course the size of the core team and diversity of contributors over that time has changed drastically so it's not comparing apples to apples. But you said you weren't aware of data to mine so I'm giving you an axe and shovel.
Perhaps drastic over the last five, but not over the last three, IMHO. Some change, but not enough to account for going from 59 completed in Rocky to 25 in Train. Not all blueprints are the same size, nor require the same amount of effort on the part of any of the parties involved. Involvement ebbs and flows with other commitments, like downstream release timelines. Comparing numbers across many releases makes some sense to me, but I would definitely not think that saying "we completed 25 in T, so we will only approve 25 in U" is reasonable.
(B) Require a core to commit to "caring about" a spec before we approve it. The point of this "core liaison" is to act as a mentor to mitigate the cultural issues noted above [5], and to be a first point of contact for reviews. I've proposed this to the spec template here [6].
As I'm sure you know, we've tried the "core sponsor" thing before. I don't really think it's a bad idea, but it does have a history of not solving the problem like you might think. Constraining cores to not committing to a ton of things may help (although you'll end up with fewer things actually approved if you do that).
--Dan