Miners are the ones with the voting power here. Specifically, that voting power is weighted based on their ability to quickly download blocks and transactions, solve blocks, and then push the blocks out to the network. Right now, this is based on their hashing ability. If the blocks start to become too large because of transaction volume, it could take minutes instead of seconds to push around all that data over networks, which would impact the speed of solving blocks. If the fees aren't high enough, the miners may decide to start pruning out transactions in order to gain a leg up on the competition. AFAIK, we aren't there yet, except for a few pools that don't include SDICE transactions.

I don't think we have a real issue until the average fee that the miners demand for inclusion in the blockchain becomes too large for most of the users on the network. The likely reaction to that would be for specific applications to move their traffic onto internal networks, which would take some load off the blockchain. If the network became too fractured, then obviously that could be a potential flaw.

And if you want to block transactions going to/from SDICE, you really ought to be convincing the mining pools to reject them or charge higher fees, since they are the only ones who can do something about it.