Does using or acting as an escrow count as mixing?
Why?/Why not?
I have observed some exchanges use (what I'm loosely referring to as) a two step wallet where you link a wallet AND the exchange's wallet. You can then shift coins backwards and forwards between the two. Essentially you can mix coins(deposit to one wallet then withdraw from the other).
Will these exchanges be banned too?
Will discussing methods of how coins could be mixed a banable offence?
No one is banning exchanges and I don't see this question and the reason on point at all. There are some businesses specifically designed for that purpose or similar purposes, but are exchanges specifically designed for that too?
After all, if there is any illegality, exchanges are well-known, they can be made accountable for everything, and having it on record makes it easy for any law enforcers, and can assist them in their investigation. Anyone following that procedure you just explained to hide their money is even only wasting their time as such is never hidden from the radar.
So why ban exchanges here too?