It is, always has been and always will be straight blue vein cheese imo. We've had many debates on this board about this supposed 'tactic'. I can't believe this wasn't fixed, now the pro-cheating camp can argue that it's a feature. My favoured fix has always been a trading reputation mechanic, which would see dishonourable deals come at the cost of future trade potential similar to what's been proposed.
If players do use this ploy and pull gold out of their hats every time they DoW then it makes domination victories, especially on deity, a LOT easier. To me it seems like it has too great an effect on your winning chances for such an asinine action. If it isn't punished in game, and we all know it should be, then I say it should be completely avoided.