I have developed this idea into a BIP which is available for people to view here. https://github.com/mechanikalk/bips/blob/master/bip-%3F%3F%3F%3F.mediawiki

Would really appreciate any additional feedback or discussion.

The TL;DR is that it is many Bitcoin blockchains that are merge mined at different difficulties with different sets of state.  This prevents sharding of PoW without causing sharding of state.  Would enable a Bitcoin like blockchain to scale to 10,000s of TPS without any centralization.

Thanks!