So the really funny thing here is the first bitcoin exchange had a Web of Trust system, and while it had it's flaws IT WORKED PRETTY WELL. It used GPG and later on bitcoin signatures. Nobody talks about it unless they were there but the system is still online. Keep in mind, this was used before centralized exchanges and regulation. It did not use a blockchain to store ratings.
As a new trader, you basically could not do trades in their OTC channel without going through traders that specialized in new people coming in. Sock accounts could rate each other, but when you checked to see if one of those scammers were trustworthy, they would have no level-2 trust since none of the regular traders had positive ratings of them.
Here's a link to the system: https://bitcoin-otc.com/trust.php (on IRC, you would use a bot called gribble to authenticate)
Not easily, but I could imagine a project deciding to trust (to some degree) people vouched for by another project whose judgement they trust. Or, conversely, denouncing those endorsed by a project whose judgement they don't trust.
In general, it seems like a web of trust could cross projects in various ways.
- a problem already solved in TFA (you vouching for someone eventually denounced doesn't prevent you from being denounced, you can totally do it)
- a per-repo, or worse, global, blockchain to solve incrementing and decrementing integers (vouch vs. denounce)
- a lack of understanding that automated global scoring systems are an abuse vector and something people will avoid. (c.f. Black Mirror and social credit scores in China)