Rather than re-enable OP_LEFT, a NOP could be re-purposed in a soft fork.

OP_DUP OP_HASH160 [pubKeyHash[:LEN_PARAM]] [LEN_PARAM] OP_LEFTEQUALVERIFY
OP_DROP OP_CHECKSIG

A B L OP_LEFTEQUALVERIFY checks if the leftmost L bytes of A and B match.
If not, then the script immediately fails.  If either array is less than L
bytes or if there are fewer than 3 values on the stack, then it also fails.

The OP_DROP is needed as the new opcode must count as a NOP for legacy
nodes.

A change like this would only cause a once-off improvement in efficiency,
so it is less likely to be worth the effort.

It also requires most clients to be updated to support the new address
system.

A different BIP could be added for that.

An alternative way to add new opcodes is to use a different script engine
like with P2SH.


On Wed, Jul 22, 2015 at 9:15 PM, Jeremy Rubin via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> While we're all debating the block size, please review this proposal to
> modestly increase the number of transactions per block.
>
> https://gist.github.com/JeremyRubin/4d17d28d5c681a93fa63
>
> Best,
>
> Jeremy
>
>
>
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>