The problem with allowing this is that abuses are very easy.
Realms could simply funnel all of their realm gold into the hands of one person and have him cover 100% of all expenses at all times. That leaves much to be desired about the system if someone chooses to do so.
How would a nation doing so benefit? I am not saying they won't, I just can not see it yet. They would have to tax all the knights at %100, and all lords at %100. How many knights and lords are willing to submit to that for the good of the realm? Or they could demand that all nobles send all extra gold to Duke X. Once again, what are the chances that they are ALL ok with that. Then, assuming they are all OK with it, how will that give an unfair advantage to the realm?
