Using zk-SNARKs, it is actually possible for commodity devices to verify the entire chain state, including the semantics of every state transition. Mina uses this architecture today, and using recursive zk-SNARKs achieves a state size of around 22kb. An architecture like this could fill a similar security role to that of light clients, with the added benefit of allowing every-day users to run a fully verifying node on their commodity device. https://mirror.xyz/suzuha.eth/vb5E5lhzmPTcpxOJcz6Q211TDgSvoFwDLA6JSM1V37Q