A block size increase “based on demand”, and leaving it to the miners to decide how large the blocks should be “based on demand” is a very dangerous proposition, topcoin360. It will open an attack vector, that would possibly disrupt the network.
As far as I understand, you do not want to allow miners to increase the block, because they will have the opportunity to hack the system. Very strange reasoning. After all, miners ALREADY have a 100% chance to hack the system. If, of course, they have such a collective desire. For example, they can start mining empty blocks. Or make a 51% attack. That's all, the system is broken.
It looks like this: a person has a full warehouse of weapons. And you : we can't give him a loaded gun. He will have the opportunity to kill someone.
The security of the bitcoin system is 99.99% dependent on the miners. And if you give them the opportunity to change the block size, nothing will change. Similarly, the security will be 99.99% dependent on the miners.
Hack the system? No, that’s not the reason. I’m talking about incentives. If you give the miners the power to decide how large the blocks would be “based on demand”, then you’re giving them an incentive to fake that demand for them to earn more on fees. Especially when most of the coins are mined out.