If ChipMixer were to, in practice, exclude users who haven't upgraded to Bech32-compatible wallets, how would that affect the anonymity set of the overall service? Would it matter, in your opinion?
The anonymity set would undoubtedly reduce, but even if it didn't, I wouldn't want to cut off some users from the service, particularly users who are using custodial wallets and are in the greatest need of privacy improving services. Even if they only offered legacy addresses for inputs, I can't see any real reason the chips for withdrawal aren't SegWit.
When you say an output could easily be identified as a CM output, I assume you are talking strictly in terms of an heuristic analysis, and not necessarily in terms of blockchain analysis, correct? That is to say, if I merged and split my own outputs exactly as I have observed ChipMixer doing and then sent you some of those chips, you would assume they came from ChipMixer.
Probably. I don't really care where my bitcoin come from, so I don't really pay much attention. If you sent me an exact chip value, and I went back one transaction and saw a "classic" ChipMixer funding structure, then yeah, personally I would probably just assume it was from ChipMixer and not look any deeper. I'm sure that if I was interested and probed a bit deeper though I could figure it out, though.