If I understand this BIP correctly, the values pushed onto the stack by the
OP_COUNT_ACKS operation depends on the ack and nack counts relative to the
block that this happens to be included in.

This isn't going to be acceptable.  The validity of a transaction should
always be monotone in the sense that if a transaction was acceptable in a
given block, it must always be acceptable in any subsequent block, with the
only exception being if one of the transaction's inputs get double spent.

The added check lock time and check sequence number operations were
carefully constructed to ensure this property.

On Sun, Oct 2, 2016 at 11:49 AM, Sergio Demian Lerner via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Since ScalingBitcoin is close, I think this is a good moment to publish
> our proposal on drivechains. This BIP proposed the drivechain we'd like to
> use in RSK (a.k.a. Rootstock) two-way pegged blockchain and see it
> implemented in Bitcoin. Until that happens, we're using a federated
> approach.
> I'm sure that adding risk-less Bitcoin extensibility through
> sidechains/drivechains is what we all want, but it's of maximum importance
> to decide which technology will leads us there.
> We hope this work can also be the base of all other new 2-way-pegged
> blockchains that can take Bitcoin the currency to new niches and test new
> use cases, but cannot yet be realized because of current
> limitations/protections.
>
> The full BIP plus a reference implementation can be found here:
>
> BIP (draft):
> https://github.com/rootstock/bips/blob/master/BIP-R10.md
>
> Code & Test cases:
> https://github.com/rootstock/bitcoin/tree/op-count-acks_devel
> (Note: Code is still unaudited)
>
> As a summary, OP_COUNT_ACKS is a new segwit-based and soft-forked opcode
> that counts acks and nacks tags in coinbase fields, and push the resulting
> totals in the script stack.
>
> The system was designed with the following properties in mind:
>
> 1. Interoperability with scripting system
> 2. Zero risk of invalidating a block
> 3. No additional computation during blockchain management and
> re-organization
> 4. No change in Bitcoin security model
> 5. Bounded computation of poll results
> 6. Strong protection from DoS attacks
> 7. Minimum block space consumption
> 8. Zero risk of cross-secondary chain invalidation
>
> Please see the BIP draft for a more-detailed explanation on how we achieve
> these goals.
>
> I'll be in ScalingBitcoin in less than a week and I'll be available to
> discuss the design rationale, improvements, changes and ideas any of you
> may have.
>
> Truly yours,
> Sergio Demian Lerner
> Bitcoiner and RSK co-founder
>
>
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>
>