This query was answered by Satoshi. My try to paraphrase: Suppose a transaction T specified an expiration peak, X, and was mined in block X. Then its outputs have been spent, presumably many instances over by means of a number of generations (the unique transaction had, for instance, great-great-grandchildren). Now a reorg happens and there is a new model of the block at peak X that does not embody T.
Most (now unconfirmed) transactions are merely re-mined within the new department, presumably at totally different block heights than earlier than. However T cannot be re-mined, since it’s now invalid (it has expired), as are all of its descendants. As Satoshi places it,
This would not be honest to later homeowners of the cash who weren’t concerned within the time restricted transaction.
It is true that any reorg could cause previously-mined transactions to by no means be mined. However such double-spending would seemingly require malicious intent — a 51% assault by miners, relatively than, say, an innocuous short-term community partition.
It might be unhealthy if this situation (a previously-mined transaction is un-mined after which expires) might occur routinely as a result of it will make funds much less sure and would give cost receivers an incentive to confirm the windfall of the cash they’re being paid with, lest they be from a recent-expiring transaction. That is just like the motivation for the 100 block coinbase maturation consensus rule.
