The mining transaction fee has to increase, but the price of the bitcoin should also increase to attract more miners.
It's inevitable that fees will increase; if we increase the blocksize right now, fees will indeed lower, but this will have a negative effect in the future when blocks are pretty much all mined. The price of bitcoin is uncontrollable, and although it's highly likely that will increase, it's not guaranteed. Most of us won't even be alive by the time blocks are all mined in terms of block reward without transaction fees; it's not a huge issue to us at the moment.
As I've been told, the transaction fees are market determined, i.e. by the "buyer". In this case, the buyer would be Bitcoin senders and not the miners. Right now, miners could simply drop the transactions if the latter didn't have enough fees (or no fees at all) and mine just for the sake of getting the reward. This is what seemed to have happened in July, 2015, when literally thousands of transactions got stuck unconfirmed (some ironically called it "testing Bitcoin limits")...
But when there is no more reward to mine for, would the miners reject transactions as easily?