Adding this to the rules would be a few sentences at most. Something like:
"If the DQ'd player has a score of 0, then the affected player will take over that position and play. Otherwise, it will be treated as a major malfunction."
It could likely be worded a little better than that, but it doesn't need to be overly complicated. There's nothing left up to the TD's discretion. If there is an open slot with a score of 0, then the affected player plays in that slot. If there is not, then the current rules apply.
I'm failing to see how any of the presented scenarios would be worse under the proposed rule change. In fact, I think the rule change would deal with them better.
All of the players would play a standard 3 ball game and this would not be a concern.
The proposed rule change further minimizes impact on the game and does not cause the TD to make a "major decision". If the situation is applicable then the rule would be applied. It's not ambiguous.
If you're playing lock stealing games, the proposed solution still maintains the original order. I don't see how it complicates things.
You can still pay attention and tell the player to stop playing before they lock balls. I also don't see how the current rule covers this better. You would get two locks for free and an additional compensation ball rather than starting with a 0 score and getting to pick your house like you do with a normal game.