{sign|verify}message replacement

In an email exchange between Jim Posen and Kalle Rosenbaum, Posen inquires about the handling of scripts with OP_CLTV and OP_CSV by verifiers. He asks whether they always succeed or whether an nLockTime and nSequence should be included in the proof in a way that can be parsed out and displayed to verifiers. Rosenbaum suggests that it is fine to assume sufficient time/height on CLTV/CSV checks since inputs are not always available. When asked if any signatures in the scriptSig/witness data would have no sighash type, Rosenbaum believes that it would just use the default (SIGHASH_ALL?) for simplicity and questions if there is a good reason to tweak it.