Interesting, that's a possibility.

I was thinking of something more akin to, say Google's pinned certificates (something which practices such as Let's Encrypt actually makes harder AFAICT):

https://security.stackexchange.com/questions/29988/what-is-c...

Or something that might be a parallel of email reputation services -- SenderBase / IronPort (now Cisco) rating email servers by their spam loads, etc.

Rather than negative reputation, a positive reputation (vouch rather than warn) might be viable. (Negative ratings systems, digital or otherwise, tend to inspire various legal assaults.)