Love this new take! In a way it feels opposite to the approach of SCOPE. There, a sequenced rollup can synchronously compose with the L1 if it finds someone willing to sell them L1 blockspace (without the rollup being “based”). IIUC here, a sequenced rollup can synchronously compose with the L1 if it finds someone that can supply the composasable transactions. In either case, you don’t need to be a “based” rollup, you just need some coordination with the L1 block building supply chain.
Assuming we’re talking about rollups with validity proofs, some questions/drawbacks around timing:
- Builders cannot credibly offer “based preconfs” until they’ve seen the slot-ending block as prior L2 transactions will change the state on them. This makes it tricky from a UX POV as the composability window is very short so maybe only builders would take advantage of it?
- For atomicity, we need to prove the L2 in real-time, then post the batches + validity proof + L1 sync composable calls all in the same L1 transaction. A concern is that real-time proving is already a feat. If you must wait to start this process until close to the slot’s end then you may have to tradeoff in other dimensions like decreasing gas limits?