Just wrote a similar thing to this. But the truth is it'll never happen. Clubs seek every advantage over their rivals, and you'd simply never get the top clubs agreeing to do this.
I am not sure about that. I know in the past Real Madrid have silently banned Raiola, I don't think they are a big fan of the idiot. Neither are Man City. You just need Real, Barca, Man Utd, City and PSG on board pretty much. Put the word on the street that Raiola is persona non grata at these clubs and top players will automatically steer clear of him. No one loves an agent so much to devoid themselves a chance to play for the big boys.
In reality, agent fee doesn't even bother me so much as tolerating foul mouthed idiots. They are paid by the clubs and their clients and you still put up with their attitude. I would much rather pay 30M in agent fee to Mendes than 25M to Raiola, just to make a point.