I wonder if this is possible as a soft fork without using segwit?
Increasing the sigop count for a NOP would be a hard fork, but such a
change would be fine with a new segwit version. It might require specific
support in the altcoin, which might be troublesome..
On 11 Feb 2016 20:05, "Tier Nolan via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> There was some discussion on the bitcointalk forums about using CLTV for
> cross chain transfers.
>
> Many altcoins don't support CLTV, so transfers to those coins cannot be
> made secure.
>
> I created a protocol.  It uses on cut and choose to allow commitments to
> publish private keys, but it is clunky and not entirely secure.
>
> I created a BIP draft for an opcode which would allow outputs to be locked
> unless a private key was published that matches a given public key.
>
> https://github.com/TierNolan/bips/blob/cpkv/bip-cprkv.mediawiki
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