And when you've done that, tada you have segwit (specifically, you get the _exact_ construction that was used in elements alpha). But a version of it with a ugly construction that requires every Bitcoin speaking program to upgrade _simultaneously_, and invalidates any pre-created nlocktimed transactions which _will_ confiscate some amount of users' Bitcoins (because some parties have been signing payments then destroying private keys as a time-lock-safe mechanism).
Isn't this a user problem rather than a protocol issue? First, the protocol doesn't specify that a user must destroy their private key when creating nLockTimed transactions. Second, since there's no guarantee that any given transaction will ever be successfully mined, it doesn't seem prudent to pre-sign transactions which sit off-chain and only become valid for broadcast and potential mining in some distant future whilst also deleting the private key. If this destructive behaviour can be condoned, it beggars belief that zero conf transactions are considered unsafe.