This does mean that the relay can carry out blocking attacks (where the consensus node submits a signature but never receives the related payload) but that’s about as bad as it gets.
I agree. There’s certainly trust assumption between mev_boost and validator. Similar to beacon_node and validator as standalone software in some client implementations today
This relies on the consensus node sacrificing its rewards for the current block in the expectation of higher rewards in the next
I think having proposer score boosting does mitigate some the concern, but certainly worth further exploration