I am afraid it won't be possible to have such a feature. It would lead to certain leagues being attacked more than rest.If you don’t do something about the power imbalance between the people who spend obscene amounts of money on the game and those who cannot afford to spend thousands of dollars a month, the game won’t be fun for the average players.
A suggestion: Make beacon and fort attacks in certain parts of the map inaccessible to people above certain levels. The power players could kill forts and beacons in their area, and lower-level players could enjoy the game in their area. This would work because if the power players couldn’t attack or defend outside their area, other leagues would have a chance.