[lawn]

You forgot the most important thing wrt scaling: everyone don't need to run a full node (store the block chain).

Most mobile wallets are light wallets, that query servers for the information on demand. It works great, but you have the risk of the server lying to you.

So the next level up is SPV wallets, which verify that transactions are included in blocks and that the proof-of-work is valid. So the cheat them you need to reproduce POW, which is very expensive, and also very secure.

This notion that everyone needs to run a full node is simply false. SPV security, and even light wallets security, is enough for almost everyone. Exchanges, payment processors and the paranoid few can still run full nodes.