I was always intending to choose a random subset of 100 once more than 100 became eligible. This creates more people who have a credible threat of retaliation: if you give someone negative trust for some stupid reason, you have reason to worry about them or a close friend of theirs negative-trusting you for a similarly stupid reason, if not in this month, then in a future month. I think that it pushes people (without forcing people) toward acting in-line with consensus, so that any retaliation against your sent negative trust always gets the sender excluded definitively.

IMO it'd be nice if in the future it's a subset of 100 among a pool of 250+.