I answered:

 

Which Jorge misinterpreted to mean that I think there will always be at least one miner willing to mine a transaction for free.

That's not what I'm thinking. It is just an observation based on the fact that blocks are found at random intervals.

Every once in a while the network will get lucky and we'll find six blocks in ten minutes. If you are deciding what transaction fee to put on your transaction, and you're willing to wait until that six-blocks-in-ten-minutes once-a-week event, submit your transaction with a low fee.

All the higher-fee transactions waiting to be confirmed will get confirmed in the first five blocks and, if miners don't have any floor on the fee they'll accept (they will, but lets pretend they won't) then your very-low-fee transaction will get confirmed.

In the limit, that logic becomes "wait an infinite amount of time, pay zero fee."

So... I have no idea what the 'market minimum fee' will be, because I have no idea how long people will be willing to wait, how many times they'll be willing to retransmit a low-fee transaction that gets evicted from memory-limited memory pools, or how much memory miners will be willing to dedicate to storing transactions that won't confirm for a long time because they're waiting for a flurry of blocks to be found.