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