I don't think such a feature would be all that difficult to develop. It could easily be setup in a way that is similar to how the difficulty changes - so that, for example, the max block size for the next 2016 blocks would be 250% of the average block size from the previous 2016 blocks.
That might not work because it will drive the transaction fee down to 1 satoshi, and that may be too low.
I disagree, especially as the block subsidy halves one or two more times. I don't think miners will confirm no/low TX fees in mass once the block subsidy is low as TX fees will make up more of the miners income
If they don't confirm transactions with low fees, then they are throwing away free money. The only way to get fees up is to make people compete for space in the block chain.
It requires an additional amount of work and an additional risk that a block will orphan for each additional TX that is included in a block. If the TX fee is too low then it will not be worth it to the miners to receive this additional small amount of money
