Didn't Slashdot have something like the second point with their meta-moderation, many many years ago?

Sorta.

IIRC, when comment moderation and scoring came to Slashdot, only a random (and changing) selection of users were able to moderate.

Meta-moderation came a bit later. It allowed people to review prior moderation actions and evaluate the worth of those actions.

Those users who made good moderations were more likely to become a mod again in the future than those who made bad moderations.

The meta-mods had no idea whose actions they were evaluating, and previous/potential mods had no idea what their score was. That anonymity helped keep it honest and harder to game.