I wouldnt worry about the fees, its quite obvious they will have to decrease them, they often adjust the fees with BTC also for this very reason.

There may be some way to dynamically change the fees automatically if the value increases, but we still have to somehow calculate the fees based on the USD or some other fiat value, otherwise we would have nothing as a reference.

The idea is when the maximum marketcap is reached, you would not have to worry about this, or at least they would not need frequent adjusting.