In the actual system,there's yet a practically hard cap,because there's a max in incomes that you can reach if all the variables are at the max(fans survey,adequate prices at the palace and so on)
That max should be raised in the different way in the various leagues,looking at the competitivity of the league...the only thing to be chosen is the way to calculate the competitivity of the leagues,which is a difficutl thing to do
Country rank surely isn't a good way to calculate the competitivity of a league,the random cup draw or the different choices about cup in the various league would influence too much the incomes of the various leaguje
Overall team skills could be put in the mix,but not as the only factor,because you can do very different value on some skills,especially on secondary skills,which often make the difference between similar players and teams;the same speech is for salaries and evaluations....but I think there should be the BBs to find the formula,we as users have to give the ideas,they have the duty to develop them ;D