Just to try to propose something more sustainable after criticizing the dynamic of the fee system here
https://bitcointalk.org/index.php?topic=2446054.0 Optional degressive fees (as a function of block number or time): The person making a transaction choose few fee values, each with a different "life time". They are included in the transaction. When life time has passed its fee would be returned to the payer. So if he's in a hurry he would choose a high fee with a 1 block life time (or 10 minutes) , maybe an other fee with 2 blocks life time, and a 3rd fee with infinite life time. Maybe all options should have a total fee degressive in time, even if the payer doesn't care about time.
I think it would requilibrate the incentives. Even if it's not the solution it could be easily implemented and be helpfull.