I've thought of doing something like this for years, you could do job references, former landlords for rent, etc... the list goes on and on. I just couldn't bring myself to build it because of that tiny thing with not being ethical.
There's money to be made in this, so someone will build it eventually. And if it works, what does this tell us about the hiring process? We can argue that fake references are unethical, of course, but I think that this lets us know that the system that allows them to succeed is fundamentally broken.