Searchers can have the ability to add more contextual information for bundles. For instance, what slots are a bundle valid for, which bundles can be broken apart/merged, what txs in a bundle are ok to fail, and more. For bundle merging, imagine an NFT mint where several searchers submit a backrun like [nft_mint_enable, mint_nft, mint_nft, mint_nft, ...]. In this case, only the highest paying bundle would win since there's only one nft_mint_enable transaction. With bundle merging, we could break bundles apart and find better ordering, either automatically or specified by the searchers with some type of flags attached to each transaction in a bundle