I think denouncing is an incredibly bad idea especially as the foundation of VOUCH seems to be web of trust.
If you get denounced on a popular repo and everyone "inherits" that repo as a source of trust (e.g. think email providers - Google decides you are bad, good luck).
Couple with the fact that usually new contributors take some time to find their feet.
I've only been at this game (SWE) for ~10 years so not a long time. But I can tell you my first few contributions were clumsy and perhaps would have earned my a denouncement.
I'm not sure if I would have contributed to the AWS SDK, Sendgrid, Nunit, New Relic (easily my best experience) and my attempted contribution to Npgsql (easily my worst experience) would have definitely earned me a denouncement.
Concept is good, but I would omit the concept of denouncement entirely.
I'm guessing denounce is for bad faith behavior, not just low quality contributions. I think it's actually critical to have a way to represent this in a reputation system. It can be abused, but abuse of denouncement is grounds for denouncement, and being denounced by someone who is denounced by trusted people should carry little weight.
IDK about this implementation ...
OVER-Denouncing ought to be tracked, too, for a user's trustworthiness profile.
Denounce also creates liability: you are slandering someone, explicitly harming their reputation and possibly their career.
I'd hesitate to create the denounce function without speaking to an attorney; when someone's reputation and career are torpedoed by the chain reaction you created - with the intent of torpedoing reputations - they may name you in the lawsuit for damages and/or to compel you to undo the 'denounce'.
Not vouching for someone seems safe. No reason to get negative.
Off topic but why was contributing to Npgsql a bad experience for you? I've contributed, admittedly minor stuff, to that ecosystem and it was pretty smooth.
What value would this provide without the denouncement feature? The core purpose of the project, from what I can tell, is being able to stop the flood of AI slop coming from particular accounts, and the means to accomplish that is denouncing those accounts. Without denouncement you go from three states (vouched, neutral, denounced) to two (vouched and neutral). You could just make everyone who isn't vouched be put into the same bucket, but that seems counterproductive.