-How is layer 2 going to strengthen the feasibility of proliferating full nodes on raspberry pi and phones, and will it help DEX?
I feel like a really big issue like a front and center issue is the reliance of exchanges on a central server for orderbook matching and offchain settlement, margin, colateralization, the data involved. Non custodial wallets aren't enough. The central servers are a vector point for centralization, counter party risk, over reliance upon high capital institutions.
Most DEXs, at least the ones I have seen/used actually rely on smart contracts that handle order settlement and locking/unlocking of tokens prior to their expiration. When a user "deposits" tokens into a DEX, they are actually "locking" the tokens, preventing the tokens from being moved unless certain conditions are met. When a user places an order on a DEX, they are signing a message that agrees to exchange x amount of y tokens for z tokens at a specific exchange rate, and if the DEX matches the order, someone on the other side of the trade will have to have signed a message confirming the opposite trade, and the tokens are moved between addresses. If the order has not been fully executed, you can cancel the order with another signed message, and the DEX will need to also sign a message allowing the order to be cancelled. The tokens are "locked" for a specific period of time that you choose when initially locking your tokens; if you want to unlock your tokens early, you can sign a transaction that must be approved by the DEX, and if the lock is expired, you can unlock the tokens by signing a transaction that does not require the approval of the DEX.
The only counter party risk to trading on a DEX is that the DEX will not allow you to cancel an order, and will not allow your tokens to be unlocked prior to the lock expiring.
Most exchanges are targets of hackers because they hold substantial amounts of customer money, however this does not apply to DEXs, so many DEXs are unlikely to be attacked the same ways that exchanges are the subject of attacks.
A layer 2 solution, such as LN could be used to reduce the cost of using DEXs, and increase the speed at which trades are confirmed. DEXs today have to settle every trade on-chain, which can very quickly get expensive. If LN was used with a DEX, trades could be settle with different LN channel states.