I'd just dread the effect it would have on RfA... It's pretty much a certainty that you'll see "'''Oppose''' Not enough people trusting" on an RfA within a week of this becoming widely used. Even worse will be the "Trusts too many people", "Trusts too few people", "Trusts User-I-don't-like, so must have bad judgement", etc. opposes.
In general, I think this idea would turn Wikipedia into a popularity contest.