Why Proof-of-Stake Sequencer Sets Are Inevitable

Today's dominant rollups rely on a single, trusted sequencer. This creates systemic risk: censorship, MEV extraction, and downtime are controlled by one entity. The sequencer is the new validator, and its centralization undermines the core value proposition of L2s.\n- Censorship Risk: A single operator can arbitrarily reorder or exclude transactions.\n- Value Leakage: Billions in MEV are captured by the sequencer, not returned to users or the protocol.\n- Liveness Dependency: The entire chain halts if the sequencer goes offline.

Decentralized sequencer sets that operate as a neutral, shared marketplace for block space. They separate sequencing from execution, allowing multiple rollups to share security and liquidity. This is the modular stack applied to sequencing.\n- Interoperability: Enables atomic cross-rollup composability (e.g., a single transaction across Eclipse, Movement).\n- MEV Redistribution: Auctions block space, creating a credibly neutral ordering layer that can redistribute value.\n- Liveness Guarantees: Byzantine Fault Tolerant (BFT) consensus ensures the network progresses.

Based Sequencing (popularized by Optimism) outsources sequencing to the underlying L1 (Ethereum), leveraging its validator set for liveness and censorship resistance. EigenLayer supercharges this by allowing Ethereum stakers to restake ETH to secure new Actively Validated Services (AVSs), including sequencer sets.\n- Ethereum-Aligned Security: Inherits the economic security of ~$100B+ in staked ETH.\n- Capital Efficiency: Stakers can secure multiple services (sequencers, oracles, DA) with the same capital.\n- Simplified Stack: Rollups avoid bootstrapping a new consensus layer from scratch.

A paradigm shift from transaction sequencing to intent fulfillment. Users express desired outcomes (e.g., "swap X for Y at best price"), and a decentralized solver network competes to fulfill them. This inverts the MEV supply chain.\n- User Sovereignty: MEV benefits flow to the user via better execution, not the sequencer.\n- Efficiency: Solvers bundle and route intents across venues like UniswapX, CowSwap, and Across.\n- Privacy: Intents can be processed off-chain, reducing frontrunning vectors.

Proof-of-Stake sequencer sets require validators to stake substantial capital, which can be slashed for malicious behavior (censorship, incorrect ordering). This creates a cryptoeconomic security floor that centralized operators cannot match.\n- Skin in the Game: Sequencers must bond $ETH or a native token, aligning incentives.\n- Enforceable Rules: Slashing conditions for liveness and correctness are programmatically verifiable.\n- Revenue Stream: Stakers earn fees and MEV share, creating a sustainable decentralized service.

Fully decentralized sequencer sets enable the final evolution: sovereign rollups. These are chains that use a shared sequencer for ordering and a data availability layer (like Celestia or EigenDA), but handle their own settlement and dispute resolution. The sequencer becomes a pure, commoditized ordering service.\n- Maximum Sovereignty: Rollup developers control the protocol's entire stack post-ordering.\n- Minimal Trust: Relies only on the economic security of the sequencer set and DA layer.\n- Interop Hub: Shared sequencing is the glue for a modular, interconnected ecosystem of chains.

A small group of large stakers can dominate the set, recreating the centralized validator problem from L1s. This leads to:

• Censorship: Ability to filter or reorder transactions.
• Governance Capture: Control over protocol upgrades and fee parameters.
• Collusion: Coordinated MEV extraction harming users.

PoS security is probabilistic and economic, not physical. A sequencer set can halt if the cost of honest operation exceeds slashing penalties.

• Stake Slashing: May be insufficient against sophisticated, cross-chain attacks.
• Chain Reorgs: Possible with sufficient coordinated stake, undermining settlement guarantees.
• Altruism Assumption: Relies on honest actors to rebuild the chain after a halt.

Each rollup's sequencer set creates a new trust domain, breaking composability and increasing bridge risk. This mirrors the issues faced by intent-based systems like UniswapX and Across.

• Trust Multiplication: Users must trust N sequencer sets for N-chain activity.
• Bridge Complexity: Forces reliance on external bridges like LayerZero or Wormhole, adding latency and points of failure.
• Sovereignty Silos: Limits the network effects of shared security models.

Most PoS sequencer sets run on forked versions of Geth or other major clients. A critical bug in the dominant client can take down the entire set.

• Single Point of Failure: Lack of client diversity, as seen in early Ethereum.
• Upgrade Coordination: Hard forks require near-unanimous participation, creating governance gridlock.
• Audit Surface: A smaller, less battle-tested codebase than major L1s.