According to an official blog post, Nethermind and Flashbots have proposed an "Alternate PBS" based on Rollups, which allows MEV revenue generated by Rollups to be obtained by the Rollup itself, rather than being paid to the proposer of the sorting chain. Alternate PBS also solves another problem related to stealing Rollup blocks. Without careful construction, proposers of the sorting chain can observe the basic Rollup blocks built by unsuccessful Rollup builders and rebuild these blocks for themselves. This allows sorting chain proposers to receive the value of building blocks without the cost of building (only copying).