However, it does not help in the context of lightning channel creation because ECDSA sigs are inherently malleable. The needed functionality is to reliably spend from unconfirmed transactions. Segregated witness can accomplish that but it is a large hard-fork change. Sighash_noinput can also accomplish that, and it is not a hard fork change. It is generally difficult to come up with features that absolutely must be implemented as hard fork changes.