In the original Lightning whitepaper, Joseph Poon advocates using
SIGHASH_NOINPUT so that we can create the first commitment transaction which references the funding transaction
txid without actually signing the funding transaction. However that paper was written before SegWit was implemented. Given that SegWit transactions do not have signature component in the
txid, it removes the need to actually implement
However, today I came across a draft proposal of the sighash in BIP 118 which says it would be active with SegWit v1 and higher.
Am I missing anything else that this sighash flag brings to the table that would warrant it to be implemented in future SegWit versions?