You're right to bring up Ark. But I have trouble with it, first because I don't understand it well (where is it documented properly, in detail?) and also it having "operators"/service providers is a big concern of mine - you're free to disagree on that, though. I really need to understand it but I hate it when there isn't a spec, or paper to read. With respect to the pools concept generally, I am not so optimistic as you, but I 100% agree it's a tantalizing area. Unless it works with *very* large numbers (I don't think 100 cuts it, for example) I suspect it won't ever go anywhere, and it's critical that it doesn't effectively require onlineness of all participants etc. I find most designs are fragile, or, they have centralization.

Docs: https://arkdev.info/docs/learn/concepts Even I don't like the use of ASPs. However, I beleive a better version of Ark can be built using maker-taker model as used in joinmarket. In coinjoin it can make transactions less likely to be identified on-chain as cj, more freedom to exit at any time and reduce interactivity.

Re the docs, I was looking at that page earlier today, perhaps unfairly dismissing it as "high level guide" when i want a detailed protocol description. If that's the most detailed description that exists maybe it works.