Are validators in the same cluster (eg same exchange, same user) more likely than unrelated validators to miss attestations at the same time? If so, can we tweak rewards to favor decentralized staking?

Possibly yes.

https://ethresear.ch/t/supporting-decentralized-staking-through-more-anti-correlation-incentives/19116

Come on, this is the absolute coolest shit. Being able to detect & penalize centralized staking?

Protocol design is so cool. I'm so bullish on ethereum. The amount of big brain thinking cycles that have gone and are going into it is insane