The problem is, TDs aren't going to impose rules that limit the field since it's not in their financial best interest. In all reality, casinos don't care where players get the money they gamble with. Until this starts affecting field sizes, it's difficult to see any authoritative body seriously addressing this.
The whole situation is complicated by the standard of proof. Even in Doug's example, we wouldn't be having this conversation if we weren't able to see Bicknell and Foxen's hole cards. This is an obvious and presumably uncommon situation where a romantically involved couple happened to make it to the final three. And while it's easy to surmise that any two experienced players would have undoubtedly and happily have gotten it AIPF here, it's impossible to say with absolute certainty that either player would have acted differently against another opponent. And you need to be able to do that if you're going to impose any sort of penalty.
I haven't read the rules of the WSOP but I'm sure there are provisions against soft playing and collusion. But the only standard that I'm aware of (aside from signalling and other physical signs of cheating) is failing to raise while last to act after the river card with the absolute nuts while heads up in a pot.
This is where public disclosure comes in. Even if you can't do anything about it, I would certainly prefer to know if there are players at the table that have a financial incentive in another's outcome. It's not a perfect solution, but it's better than nothing.
I doubt banning players from staking other players that are playing in the same tournament as them will affect field sizes at all. On the flip side, encouraging staking from the public will increase field sizes, which is a good thing for the game.
So I'm a supporter of staking, but only if its done in a way that doesnt harm the integrity of the game. And staking is going to happen regardless. Why not build a rules framework around it, and get it to work in the best interest of the game.
Rules framework mission = 1) protect the consumer 2) create a fair playing field for the players 3) grow interest/support for the game