I think if you would like to convince others that this is viable, you need to explain how abuse will be taken out of the equation.
Simply: possible abuse of power is on both sides of the equation.
It doesn't matter if you trust user X when it comes to witness votes decisions.
Or if you trust user Y about being a good witness.
If you trust X as a proxy and X votes for Y, it is exactly the same as if you would trust Y as a witness. If there is some malicious agenda at X or Y, then issue is the same: you chose to trust wrong people.
Not to mention that you have complete control on your decision and that can be changed in 3 seconds.
Witness is not my point at all, I think you understand that. A witness, if voted to be a witness by each account, has earned the right to be witness. If one person could cast 1000 votes for those who otherwise don't care to vote, that is an imbalance that should not be readily welcomed.