It's all about scaling. Hal mentions in his email that "Bitcoin itself cannot scale to have every single financial transaction in the world be broadcast to everyone and included in the block chain". This is the main topic. Today transactions roll up to the Banks and then they settle between themselves. Think ACH or credit cards. Lightning in a way models this. Each node in the hops between the payer and payee settle between themselves. Federated e-cash is another layer that abstracts a similar model. The key is the money. We need to get off Fiat and onto Bitcoin as the base money layer. The scaling solutions all have trade-offs, but that is very much secondary to the base money layer.