Miners can include the final transaction, with high fees, that will be broadcasted by the last user. They don't have to participate in transaction batching, if they don't want to.
Then, it is all about regular, non-mining nodes, and their ability to find transactions, which could be open for modifications, and joining them, and then broadcasting a different version through full-RBF.
This all sounds like a theory based on the technical capabilities of what the Bitcoin network can do. But as I asked earlier, does this happen in practice? Do you have proof and examples of transactions where individuals engaged in batching and/or modifying transactions with the aim of decreasing their on-chain size? Are there forum threads, communities or blog posts where this approach is explained in more detail and where people have testified that it works?