Interoperability of state and value is likely to place downward price pressure on layer-1 blockchains that have no monetary premium, while enabling strong middleware protocols to achieve cross-chain, winner-takes-most dominance in their respective services. While not a perfect mapping to traditional use of the term middleware, these protocols can be thought of as anything sitting just below the interface layer (i.e., the applications the end user interacts with), but leveraging the lower-level functionality provided by layer-1 blockchains and interoperability protocols.
Others have called these service-layer protocols, as they focus on providing a specific service to the interface layer, be they financial, social, technological, etc. Financial services include things like exchange, lending, and risk-management; social services offer functionality like voting structures, arbitration, or legal-contract management; technological services include components like caching, storage, location, and maybe the granddaddy of them all, a unified OS for protocol services to be neatly bundled to the interface layer.
Financial-service protocols that Placeholder has invested in include 0x, Erasure, MakerDAO, and UMA, while Aragon is our main social-service protocol to date, and technological-service protocols that we work with include CacheCash, Filecoin, FOAM, and Zeppelin. All of these protocols have originated on Ethereum, but we believe interoperability of state and value—the promise of a Cosmos, Polkadot, and Ethereum 2.0 future—will allow these protocols to become horizontally defensible starting from Ethereum’s base.
Take MakerDAO, for example. Its token, MKR, can be thought of as an insurance pool for secured loans originated through the platform. The larger the overall value of MKR, the greater the insurance and therefore lower the risk for all users of the system. Let’s say FakerDAO pops up on Tron, providing the exact same service, but with its own native governance asset, FKR. Right now, it would be hard for the Maker team to leverage the value in MKR to secure a parallel system on Tron, but with interoperability of state and value it would become considerably easier.
Assuming the Maker team can build out for Tron before FKR gets to a similar value as MKR, then they should be able to deploy on Tron and provide a lower risk service than FakerDAO can, insured by the much larger pool of value stored in MKR. With two communities driving utility through MakerDAO, MKR’s pooled value is then likely to significantly outpace FKR’s, further widening the risk and quality of service-gap (Whether MKR holders would want to underwrite the risk of operating on another chain like Tron is a separate question).
We believe similar dynamics will play out for many other middleware protocols, though in different ways depending on the cryptoeconomic  and governance design of the system. Protocols whose reliability, security, speed, liquidity, or coverage scales with the size of the asset base and nodes supporting it, stand to do well in an interoperable world.
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 Most middleware protocols are likely to employ some variant of a capital asset as their cryptoeconomic model, where supply-siders must stake the asset to provide the service, giving them access to value-flows for so doing.