I don't like this 75% full idea because the miners would virtually be REQUIRED to pad out blocks with trivial transactions if they don't have enough on their own. To not do so would leave hashing power idle.
A simpler solution would be to require that blocks are always 1 MB (or whatever) in size, and that they must be padded out with 0xDEADBEEF or whatever if the block can't be filled with transactions. This way all blocks will take the same amount of time to transmit, and there's no incentive not to include a transaction of any fee if what it's replacing would just be bad data.
I'm not saying I'm in favor of this proposal necessarily, but it works better.
A simpler solution would be to require that blocks are always 1 MB (or whatever) in size, and that they must be padded out with 0xDEADBEEF or whatever if the block can't be filled with transactions. This way all blocks will take the same amount of time to transmit, and there's no incentive not to include a transaction of any fee if what it's replacing would just be bad data.
I'm not saying I'm in favor of this proposal necessarily, but it works better.