We could however introduce a new field in a new tx version. We know we need to rev the format at some point anyway.
On Wed, Aug 6, 2014 at 2:55 PM, Jeff Garzik <jgarzik@bitpay.com> wrote:
...and existing users and uses of nLockTime suddenly become worthless, breaking payment channel refunds and other active uses of nLockTime.
You cannot assume the user is around to rewrite their nLockTime, if it fails to be confirmed before some arbitrary deadline being set.
If nLockTime is used for expiration, transaction creator can't lie to
help tx live longer without pushing initial confirmation eligibility
into the future. Very pretty. It would also enable "fill or kill"
transactions with a backdated nLockTime, which must be confirmed in a
few blocks, or start vanishing from mempools.