Governance forms a whitelist of sequencer operators ala Lido, and we rotate between them every epoch (e.g. X hours). Optimism Foundation retains rights as a reserve sequencer if the lead sequencer is offline. Can ask them to post up a bond in OP or ETH.
Next step, whitelisted operators can participate in an auction, more sophisticated penalties/incentives. Final step: remove the whitelist, or implement whatever the final decentralization mechanism.