If I'm not mistaken, bidbot owners will be fine under your system, as they will make a better return than they currently make.

Most bidbot owners have large stakes because it's delegated to them. The delegators will do well when they remove the delegation, but it will remove all the value from running a vote-selling service. The bidbot owners will still get value from the SP they've managed to accumulate themselves, but most of their income comes from selling the votes of other people.

On the other hand, I see no reason why the controllers of the @steemit account would go along with this, since I presume they consider they own this stake, and it is not communal property.

That's really complicated. Essentially there's a community expectation that Steemit Inc. will not use that stake; as such they leave it sitting at 100% voting power all the time, and have shown no inclination to change that. My solution essentially just leaves them doing the same thing in a different fashion.