I listened to a talk at zksummit7 titled "Web3 Foundation Accountable light clients via BLS multisignature rollup" given by Alistair from web3f. My interpretation of the talk is that Alistair and his team have developed a zkp + BLS multisig mechanism for building accountable light clients. The zkp circuit is used to keep track of the active validator set and the BLS multisig is used to aggregate finality vote sigs. I think this is the most promising approach I have seen to date for building a trustless substrate / polkadot light client. I am very keen to learn more about this. I have reached out to Alistair via his web3f email but no success. I wonder if anyone has any additional resources / insights that they could share on this topic?
I have found the slides from zksummit7: https://drive.google.com/file/d/1BrKuqib5msj_M_kiCorSYWBFvP9VlTCg/view?usp=sharing
The slides reference the github repo: https://github.com/w3f/apk-proofs
Of relevance is the application of this construction for a light client example: https://github.com/w3f/apk-proofs/blob/main/bw6/examples/recursive.rs