Interoperability is a characteristic of a product or system, whose interfaces are completely understood, to work with other products or systems, at present or in the future, in either implementation or access, without any restrictions.
Interoperability is the capacity of computer systems to exchange and make use of information. It is the capacity of systems to collaborate with each other, where collaborating in this sense entails the ability to transfer information or an asset between two or more systems while keeping the state and uniqueness of that entity consistent.
The challenge is that one consortium designs and implements what is best for them given the use cases they are looking to address.
Any incentives to ensure interoperability will always be secondary to that. Essentially, you prioritize short-term incentives (build something to prove the use case) for long-term initiatives (build something that will work with new or existing use cases on other complementing platforms).
Arbitrary data exchange
Put simply, exchanging arbitrary data is the capacity to do something on one blockchain platform that affects another blockchain platform. What is tracked is not necessarily an item of value but could be an event. From a technical perspective, this means making blockchain-to-blockchain application programming interface (API) calls, which can go as far as having smart contract code on one blockchain platform verify the consensus finality of events on other blockchain platforms directly. This capacity allows the use data on one blockchain platform to affect state changes on another. It also lets us create synthetic versions on one chain of an asset that is home to another chain, making that asset usable on a state machine that occupies a different part of the trade space. As most blockchains are passive systems unable to produce a verifiable-by-others signature, arbitrary data exchange is the more difficult type of interoperability to achieve. However, the use cases enabled by arbitrary data exchange can be more advanced than what digital asset exchange makes it possible.
An example of arbitrary data exchange is the changing ownership of a bill of lading (BoL) from a shipper on Ethereum to a consignee on Hyperledger. The BoL is a document of title. Currently, the BoL is typically issued from the ocean carrier to the shipper/seller as proof of receipt of the container and contains data on, for example, the shipper, the consignee, the notified party, the vessel voyage, the vessel name, the container ID, goods description, trade terms, signatures, stamps, and BoL number. The document is typically kept with the shipper/seller until payment for the shipment has been received from the buyer. The document can be changed multiple times if, for example, the shipment misses its route, if the notified party changes, if the buyer changes and the consignee needs updating. Moreover, banks typically hold a copy of the document as security for loans in relation to trade finance.