Christian suggested that the use of sighash flags that are not SIGHASH_ALL is a remaining venue for malleability. However, Luke argued that signer malleability is still a notable concern needing consideration, as wallets should be trying to actively CoinJoin, bump fees on, etc any pending transactions in the background. He proposed specifying flags upfront in the UTXO-creating transaction specifying which parts the signature will cover, allowing implementation of fully malleability-proof wallets. Christian asked how signer malleability is still a problem if signatures are removed from the transaction ID of the transaction and all preceding transactions. Luke responded that it is still possible to double-spend transactions that do not have enough fees, so starting a new round of CoinJoin is sufficient to bump fees for all parties that participate, and that would also result in the double-spent low fee transaction to be discarded, resolving the state of all coins in the first CoinJoin tx.