Shared Sequencer

Shared sequencers can make cross-rollup interoperability faster and cheaper. Interoperability between rollups (messaging) is a separate process from the sequencer tx ordering and batching.

Drawbacks:

However depending on the number of rollups using a shared sequencer, cross-chain communication or liquidity transfers may be more efficient via third-party bridges than sequencers in some cases.

Source: @ayyyeandy from The Rollup