I feel it is breaking a principle that if a transaction is valid it remains
valid. There might be dangerous repercussions to breaking that rule. For
instance chain of transaction become invalid which might lead to losses.

On Thu 6 Sep, 2018, 6:37 PM Alejandro Ranchal Pedrosa via bitcoin-dev, <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Hello everyone,
>
> We would like to propose a new BIP to extend OP_CSV (and/or OP_CLTV) in
> order for these to allow and interpret negative values. This way,
> taking the example shown in BIP 112:
>
> HASH160 <revokehash> EQUAL
> IF
>      <Bob's pubkey>
> ELSE
>      "24h" CHECKSEQUENCEVERIFY DROP
>      <Alice's pubkey>
> ENDIF
> CHECKSIG
>
> that gives ownership only to Bob for the first 24 hours and then to
> whichever spends first, we basically propose using the negative bit value:
>
> HASH160 <revokehash> EQUAL
> IF
>      <Bob's pubkey>
> ELSE
>      "-24h" CHECKSEQUENCEVERIFY DROP
>      <Alice's pubkey>
> ENDIF
> CHECKSIG
>
> meaning that both would have ownership for the first 24 hours, but
> after that only Bob would own such coins. Its implementation should
> not be too tedious, and in fact it simply implies considering negative
> values that are at the moment discarded as for the specification of
> BIP-112, leaving the sign bit unused.
>
> This, we argue, an increase the fairness of the users, and can at times
> be more cost-effective for users to do rather than trying a Replace-By-Fee
> transaction, should they want to modify such payment.
>
> We would like to have a discussion about this before proposing the
> BIP, for which we are preparing the text.
>
> You can find our paper discussing it here:
> https://hal-cea.archives-ouvertes.fr/cea-01867357 (find attached as well)
>
> Best,
>
> --
> Alejandro Ranchal Pedrosa, Önder Gürcan and Sara Tucci-Piergiovanni
>
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