Why MEV-Boost Was Just a Prelude to Shared Sequencing

A single entity controlling transaction ordering is a single point of failure and a massive honeypot. This centralizes power and creates perverse incentives for censorship and maximal value extraction.

• Security Risk: A compromised sequencer can halt the chain or front-run its own users.
• Economic Capture: The sequencer captures all MEV, disincentivizing user participation.
• Fragmentation: Every rollup building its own sequencer is a massive capital and operational waste.

Shared sequencers like Espresso, Astria, and Radius decouple execution from ordering. They create a competitive marketplace for block building, similar to MEV-Boost but at the sequencing layer.

• Interoperability: Enables atomic cross-rollup composability, unlocking new DeFi primitives.
• Economic Efficiency: Sequencer costs are amortized across many rollups, reducing overhead.
• Liveness Guarantees: Decentralized validator sets or fast failover mechanisms prevent chain halts.

Ethereum's Proposer-Builder Separation (PBS) via MEV-Boost proved the model. It showed that separating block proposal from block construction creates a healthier, more efficient ecosystem.

• Validated Model: $2B+ in MEV has flowed through the PBS market since Merge.
• Specialization: Builders like Flashbots and bloXroute optimized for complex orderflow, a template for shared sequencer operators.
• Reduced Centralization: Prevents the "wealthiest validator wins" dynamic from poisoning the L2 landscape.

Shared sequencing is the prerequisite for intent-based architectures. Users express a goal ("swap X for Y at best price"), and a shared sequencer network coordinates execution across domains via projects like UniswapX and Across.

• User Abstraction: Eliminates manual chain bridging and gas management.
• Optimal Execution: Solvers compete across rollups and L1s to fulfill the intent.
• Unified Liquidity: Treats the multi-rollup ecosystem as a single venue, mirroring CowSwap's batch auctions on L1.

MEV-Boost created a builder cartel with ~90% of Ethereum blocks. Shared sequencers risk a similar fate, where a single dominant network like Espresso or Astria becomes the mandatory gateway for dozens of rollups. This creates a single point of failure and censorship for the entire modular stack, worse than L1 validator centralization.

• Risk: Replaces L1 consensus with a new, more concentrated trust layer.
• Outcome: Rollups trade sovereignty for convenience, enabling cross-rollup MEV extraction at scale.

Pushing sequencing off-chain fundamentally weakens Ethereum's security model. If a shared sequencer withholds blocks or goes offline, hundreds of rollups stall simultaneously. The L1 cannot reconstruct the canonical chain, creating systemic risk. This inverts the security hierarchy, making the entire ecosystem dependent on a new, less battle-tested component.

• Risk: Settlement finality is gated by an external, potentially Byzantine sequencer.
• Outcome: A sequencer failure triggers a multi-billion dollar liquidity freeze, worse than any single L1 outage.

A profitable shared sequencer has zero incentive to innovate or reduce fees. It becomes a rent-extracting toll booth, mirroring the problems of high L1 gas fees. Competitors like decentralized sequencer pools (e.g., based on SUAVE) or alt-L1 sequencers will be locked out, stifling the competitive forces that drive fee reduction and technological progress.

• Risk: Monopoly pricing for block space across all connected rollups.
• Outcome: Innovation shifts from public goods to capturing the sequencing market, benefiting VCs over users.

Instead of unifying liquidity, competing shared sequencer networks (Espresso, Astria, Radius) could create new silos. Rollups on Sequencer A cannot trustlessly communicate with rollups on Sequencer B without a bridging layer, recreating the cross-chain problem with extra steps. This defeats the core purpose and adds meta-MEV opportunities between sequencer domains.

• Risk: Walled gardens of rollups emerge, fracturing composability.
• Outcome: Developers must choose an ecosystem, not a chain, locking in value and users.

A centralized sequencer processing transactions for major DeFi apps is a juicy target for regulators. It's a clear, legally identifiable entity that can be forced to censor transactions (e.g., Tornado Cash) across hundreds of applications with one order. This creates a systemic censorship vector far more efficient for authorities than targeting individual dApps or validators.

• Risk: OFAC compliance becomes trivial to enforce at the sequencing layer.
• Outcome: Permissioned DeFi by default for any rollup using a compliant sequencer.

Shared sequencing adds a new critical consensus layer between L1 and rollups. This dramatically increases the attack surface and engineering overhead for rollup teams, who must now audit and trust an additional Byzantine system. Bugs or exploits in the sequencer (e.g., ordering bugs) could corrupt the state of every connected rollup simultaneously, a catastrophic failure mode.

• Risk: Systemic smart contract risk introduced by sequencer logic.
• Outcome: Security audits shift from rollup code to obscure sequencing protocols, increasing costs and failure points.