@bruno_f: I think I concede your point—it’s possible for non-based rollups to enjoy the full censorship resistance benefits of Ethereum L1, all while enjoying preconfirmations 
Thank you for bringing this up—a significant update to my mental model! If liveness is not one of the fundamental advantages of based sequencing then I guess the two big remaining advantages are a) credible neutrality, which is critical for a shared sequencer and b) L1 compatibility, necessary to have synchronous composability with L1 contracts and $0.5T of assets.
I think my favourite preconfirmation design so far is preconfirmations that are conditional on the L1 state. That is, if the L1 reorgs then the corresponding preconfirmations no longer apply. I believe these L1-conditional preconfs work fine because a preconfirmer at slot n can offer two types of preconfirmations in parallel: preconfirmations assuming the block at slot n-1 doesn’t get reorged, and preconfirmations assuming the block at slot n-1 does get reorged (e.g. falling back to the block at slot n-2 being the parent block). There can also be an insurance market to hedge users against reorgs (which should be rare, especially with single slot finality).