Miners are sufficiently incentivized to choose an appropriate block size. Too big and their chances of being orphaned increase. This is the decentralized solution for a decentralized system.
I'm not sure if you're thinking of "no block size limit" or BIP100, I'm guessing the latter. As a miner myself, and from keeping an eye on the mining field, I can tell you that giving miners this kind of power might lead to some very odd behavior. Most of the companies and pools should not be trusted with that kind of power. It's no point with incentives if you don't understand the consequences of your actions. Just look at Ghash.io's 51% attack scare last summer. There's also the fact that we have no idea who the big actors in the field will be in five years time, nor their motives. The devs need to find a clearly defined solution and implement it. Preferably before we hit the wall.
I meant the former. BIP100 adds a convoluted voting mechanism in an effort to mimic what the free market would do on its own. Go ahead and look at the Ghash debacle, it will show you that mining isn't quite as centralized as it appears.
The miners already have the power, it's just that right now Core serves as a veneer of "community" central control. The same factors that prevent malicious mining behavior (killing the golden goose and mutually assured destruction) will work in this case too.
On the "before hitting the wall" vs "after"... wholeheartedly agree.
Ok, if you were thinking of the former then my objections don't really apply.
