The problem is that such a system could be easily abused or misused. A bad actor could intentionally or mistakenly penalize users, which would have global consequences for those users. So we need a web of trust for the judges as well, and some way of disputing and correcting the mistake.
It would be interesting to prototype it, though, and see how it could work at scale.
I don't see this ever happening, though.
I don't think there should be any judges (or to put it differently, I think every user should be a judge), nor any centralized database, no roots of trust at all. That way it doesn't present any high value targets for corruption to focus on.
The trustworthiness of a user in some domain (won't-DOS-your-page could be a trust domain, writes-honest-product-reviews could be a domain, not-a-scammer, etc) as evaluated by some other individual would have to do with some aggregation of the shortest paths (and their associated trust scores) between those to users on the trust graph.
There is no trust score for user foo, only a trust score for user foo according to user bar. User baz might see foo differently.
If you get scammed, you don't revoke trust in the scammer. Well, you do, but you also go one-hop-back and revoke trust in whoever caused you to trust the scammer. This creates incentives towards trust hygiene. If you don't want people to stop trusting you, then you have to be careful about who you trust. It's a protocol-level proxy for a skill we've been honing for millenia: looking out for each other.
But it doesn't work if there's just a single company that tracks your FICO score or something like that. Either that company ends up being too juicy of a target and ends up itself becoming corrupt, or people attack the weak association between user and company such that the company can't actually tell the difference between a scammer and a legit user (the latter is the case for the credit score companies, hence: identity fraud).
Attacks like that are much harder to pull off if the source of truth isn't some remote database somewhere and is instead based on the set of people you see every day in meatspace.
They're the only solution that doesn't require a pre-existing trust relationship, but the web is more of a dark forest every day and captchas cannot save us from that. Eventually we're going to have to buckle down and maintain a web of trust.
If you notice abuse, you see which common node caused you to trust the abusers, and you revoke trust in that node (and, transitively, everything that it previously caused you to trust).