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.mdCode & 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.