Thanks for your feedback, that’s a good point to consider. Note though that there is a strong disincentive for proposers to skip block submission since they would miss out on the block reward and could potentially be penalized for not acting on their commitment.
I agree that decryption during the block proposal stage is not ideal but that’s the best we can currently do without changing the Ethereum protocol. As we wrote in our roadmap, an in-protocol solution should be the long-term goal. Until then, this proposer-commitment approach (or similar out-of-protocol approaches) could be a promising short- to medium-term solution.
Also note that this anti-collusion mechanism is not inherently tied to proposer commitments. It could be useful in other settings or taken into account for future encrypted mempool designs that do not rely on proposer commitments.