Why make out they want this for cat JPEGs. It's about contracts for bridges right? What option is going to limit the ability to have permissionless money the most? If bridges need to contact miners directly, then only bridges that are in the interest of the majority of mining power get in. Other things, like privacy chains that are banned by the state will be rejected out of fear of prosecution. Cat JPEGs are already there with a segwit witness discount. They don't need this to bloat the chain and put pressure on decentralisation of node running. As the OP points out, currently large miners are being contacted directly to include these transactions, this works against mining decentralisation. By all means think through the consequences, but be honest when weighing up the positives and negatives. The current state of play limits bridges to white listed entities and mining centralisation. Appealing to the boogie man what if and cat JPEGs is not a strong argument.