the only way this could be enforced would be to come up with a system that could enforce 1 user, 1 account.

How to achieve that, while keeping the level of anonymity people would like to have. I have absolutely no clue.

In other words, a witness could create a @fakewhaleaccount - clean his holdings thru an exchange like binance (obfuscating the source) and vote himself back as a witness, and no one would ever know.