I like the idea of adaptive blocksizes.
I also favor the idea that capacity should always outpace demand, so I think the increases have to be substantially greater than this. I think Ethereum does it in a smart way. If I am correct, it is something like 20% more than a moving average of actual capacity used. This ensures blocks keep getting bigger as needed.
How do you differentiate real demand from spam demand?
If someone like Ver decides to dump millions of dollars worth of spam transactions in order to make the blockchain huge, how do you stop this? since if it's automated, the blockchain will just adapt to this demand (even if its fake) centralizing the nodes as a result.
I just don't see how flexible blocksize schemes aren't exploitable.
Well, i think the flexibility goes both ways -- blocks can get smaller again if the space isn't being used. That's the beauty of flexible blocks.
If someone wants to use the blockchain, and pay for it (spend millions), whether or not the transactions were useful to anyone else is kind of irrelevant. One man's spam is another man's legit use. But if they pay the fees and the miners agree to it, I think its ok and we shouldn't be trying to constrict the blocksizes because of it. Better to get a little bit of bloat and make the spammers pay for all that volume than to constantly punish everyone else with high fees and restricted capacity.