In the future the cost of transactions with bitcoin will be similar to now, the reason is simple, it may be that in the future the price of bitcoin is high then their fees will be high and if the price is low, the fees will not be so high, not only in mining, because there may be many miners with very large solar cells but in the same way the Exchanges will charge their corresponding fees according to the bitcoin price for the moment.
Yes, most of the people are concerned about the fee, definitely, there will be a high fee if the price of Bitcoin start increasing automatically the price of the transaction will surely increase. Yes, even exchanges will charge the same fee but the value of the transaction will fee will be high corresponding with the $.