If i were to suggest a cap, it would be a cap at 1.5x the revenue of the given team, and not 2x the payroll of teams in the league. The idea ought to be keeping people from spending well above their means, with or without cash banked.
However, i am not sure that this is the best idea given that it may tax the engine on updates, nor am i sold that we need to prohibit people from playing the game in their own way all that much other than punishing last minute buys.