The bip-taproot proposal specifically disallows all SIGHASH that is not the current set of valid SIGHASH flags when using this path, and thus does not include SIGHASH_NOINPUT/SIGHASH_ANYPREVOUT. New SIGHASH types are allowed in bip-tapscript (i.e. when signing for a OP_CHECKSIG variant inside a taproot script), and this is where the proposal of aj builds upon. ZmnSCPxj believes there is no point in using the collaborative path unless they are cooperatively closing. He further added that once they are cooperatively closing, they can agree to spend the funding txo without requiring that SIGHASH_ANYPREVOUT be used since they already have fallbacks in case of cooperation failure, i.e. the existing update/settlement txes.