Ini my opinion all transactions have a cost, only one comfermation per successful transaction,the transaction costs for the miners that make the transaction connect to recever so that the higher the transaction cost easier and faster. bitcon transactions are applied as incentives for bitcoin miners.
This will surely be the future, as block reward gets lower and lower. Right now you get 12,5 btc for a block, while on average a block contains 2000 transaction, at a current average 4$ fee per transaction (in the beginning of 2017 it was just 0,5$). So while a miner gets about 8000$ from fee per block, he still get 90.000$ for the block itself. The incentives for miners are by far still the block reward itself.