Ah, forgot one more issue left:
In spec/implementation, we only pass around a single nonce per round. This is correct unless you use the “optimistic” updates from “simplified update” protocol proposed originally by Rusty. In other words, you can never send updates out of turn, with the associated latency. You have to prod your counter-party to give up their turn first and wait for them to respond. To fix the out of turn optimistic updates, you would need another nonce and associated logic to manage it safely.
I never implemented the optimistic sending of updates, but didn’t ban it outright and it’s still in the spec: https://github.com/instagibbs/bolts/blob/a17b60f42077a785c625430e8f6e8e2828d4d898/XX-eltoo-peer-protocol.md#eltoo-simplified-operation