Exactly, we can use much simpler contracts than LN to provide the trade between the shares on p2pool and BTC. We do need atomicity in the trade though. So miner's shares and buyers BTC are swapped or not, there should be no state in each either of the party is left hanging.

I wonder if we should write down the contracts in the case of doing this swap without ecash and then with ecash. The devil is always in the detail. I am curious how much extra code complexity we need to introduce to use ecash here.

Another point to keep in mind is, since p2pool is a block chain with transactions, we can provide an extra op code in the script engine. So, can we make the transactions even less expensive on the bitcoin chain by using something like CSFS on the p2pool chain? My intuition says it should be possible, but I haven't explored this yet. Still in the weeds of building the p2pool chain.