When I first heard of the auction rule, I thought it was great.
But having experienced it now a few times, I find that what often happens, is that one player picks a particularly bad tribe (for that map), and then starts bidding heavily for a better tribe.
Now I understand that this can add another interesting strategic element to the game : try to stick someone with a bad tribe, and see if he blinks in the bidding.
But I do think it is kind of contary to the intention of the auction, namely: to prevent the players who have to pick later from having a disadvantage in picking the best tribes.
So I wonder if the following improvement to the auction was ever considered : whenever someone bids zero for a tribe that he did not pick himself, he is allowed to change that tribe to one of the tribes that was not in the initial selection.