>
> That would also introduce the anomaly of a script that was once valid
> becoming later invalid, when nothing varies other than time.  That is
> not super compatible with the current model of reprocessing
> transactions in later blocks if the block they were first in gets
> reorged.
>

Very good point.


>
> (Not a huge flexibility loss as you can implement "not after" by
> making it the previous holders responsibility to spend a "not before"
> back to themselves.)
>

Do you mean something like the below?

scriptPubKey:
  IF
    {A's pub} CHECKSIGVERIFY
  ELSE
    {curr_height + 100} CLTV {B's pub} CHECKSIGVERIFY

This ensures that Alice has to spend the output in the next 100 blocks or
risk it being taken from her (she just has to put an OP_TRUE on the end of
her scriptSig). So, it seems we can forget about an inverted CLTV/CSV,
great!

Best,
Stephen