Why don't people pool their gold into one hero?
The most efficient way to win a game is to give one person all the gold or kills isn't it? This creates a superweapon on your team that will demolish the enemy. And no, I actually don't think the adc is the best person to give all the gold to. The marksman is too vulnerable to assassination. I'd give it to someone like Akali, Diana, Irelia, Fizz etc. Someone with 1v5 potential. Someone tanky or slippery.
It's a design flaw inherent in the game that I'll bet people in ranked 5's could exploit to climb like crazy.