I think you misunderstood what I was writing. In some future scenario where 99.9% of transaction pay a 0.001 BTC fee or more to get into the next block and the mandatory fee is 0.00005 BTC the mandatory fee is no longer serving a purpose. It can simply be removed completely. The purpose of the mandatory fee is to prevent a spam attack and if there is enough real competition for block space such that actual fees are higher than the mandatory fee it is redundant.
The minimum fees will still serve a purpose, otherwise spam attacks and zero-fee opportunists will ensure blocks are always full even during lulls or non-busy times.Not if a miner doens't include them. As miners get more and more sophisticated I doubt you will see many including giants numbers of spam-like free tx especially when the block subsidy is negligible and they are doing extra work to hurt the network for no profit. Still it doesn't really matter if it never gets dropped (remember it is just client level rule, the protocol doesn't care). Fast forward 10 years I predict most people won't even know/care about the so called min tx fees as most tx will need to pay a fee to have timely service and clients will be in good communication with pools of miners to educate users on what fee is necessary (mandatory or not) in order to ensure timely inclusion.
