Age of Scale: How Can Blockchain Systems Become Powerful Enough for a Global Audience?

Namely, any entity needs the ability to transact with any other entity, regardless of the relative places they end up after the state space is compartmentalized.

Sharding with proof-of-stakeSharding attacks the problem head-on: instead of having every node replicate the entire state, let's break it into segments and spread them between groups of nodes.

How to process cross-shard transactions, since most nodes only keep the state within their shard?

For a node that only keeps state from its shard, how does it know with certainty that the state from other shards is consistent with protocol rules and is immutable?

Delegated proof-of-stakeThis design only has a handful of master nodes that validate transactions, emit new blocks, and promise to hold the full current state.

General purpose interoperabilityWhat if there was an inter-blockchain protocol to deliver in a trustless way transactions and state from any blockchain to any other blockchain?

The elephant in the room is that it should handle forks and chain reorgs so that the logic on arbitrary blockchains relying on external state does not break.

Having contracts with both state and held assets presents a tough theoretical problem, as every proposed scenario for who and how exactly could contest a smart contract state in case of someone's Byzantine behaviour have been prone to attacks.

If one adds or sees a transaction to a leaf, they need to have a strong expectation that the branch will stay inside the consensus state, which probably means that more transactions need to extend it.

While we do not expect a fully production-ready protocol with horizontal scaling and arbitrary state - even a largely centralized one - powerful proof of concepts and minimally viable solutions are likely to hit the market soon.