A based rollup could automatically (implicitly) use the previous L1 block hash as the latest known L1 block hash. If the L1 and L2 block proposers are identical, then the previous L1 block hash is known to the block builder, and L2 block inclusion is guaranteed.
My concern would be in these two cases:
- Permissionless fallback: L1 proposer did not opt in to propose the next L2 block so someone else needs to propose it, inclusion in the next L1 block is not guaranteed.
- L1 reorgs automatically lead to L2 reorgs.
In these cases, the “latest known L1 block hash” is either not known in advance or might change, which can invalidate preconfs.