The problem with Bitcoin is that nobody has found and it may well be impossible to find a way to develop a fee market, in the, absence of a block subsidy, that does not over time converge to one of two undesirable results: Fixed blocksize and infinite fees or infinite blocksize and zero fees. Mike Hearn has made a very persuasive argument as to why a fixed blocksize and infinite fees is such an undesirable outcome; however I am sure that Gregory Maxwell can make an equally persuasive argument as to why an infinite blocksize and zero fees is an equally undesirable outcome.
The way out of this dilemma is to allow users set
their own limits on the blocksizes they're willing to accept.
Users can't set the block size, because it is a global setting for all users in a single longest chain rule. You would need to attempt something like Raiblocks' design where every user has their own block chain, but in my analysis Raiblocks is fundamentally flawed (which can be discussed if monsterer creates a new thread to discuss various variants of models for a concensus model of transaction state).