Ethereum

not sure i'm looking at this correctly, but

would it make sense architecturally to have a hybrid between state channels and zk-rollups where only a subset of the txs are sent to main (i.e., for the state channel-like activity only send the opening/closing states, but store the rest on the L2)?

I feel like this gets close to fractal rollup designs, where you can have a "main" L2 and some validiums on top of it as L3s. Starkware introduced iirc it https://starkware.co/resource/fractal-scaling-from-l2-to-l3/, zkSync also has hyperchains

I feel like this gets close to fractal rollup designs, where you can have a "main" L2 and some validiums on top of it as L3s. Starkware introduced iirc it https://starkware.co/resource/fractal-scaling-from-l2-to-l3/, zkSync also has hyperchains https://blog.matter-labs.io/introduction-to-hyperchains-fdb33414ead7

Robust Incentives Group @ Ethereum Foundation

https://rig.ethereum.org

A validium isn't exactly a state channel, but maybe close to that in spirit