There are probably more then a few people on this board sitting with 50+BTC from the early days who could setup a coordinator
Setting up a coordinator doesn't cost any
BTC, a coordinator just sends messages back and forth to coinjoin participants.
Once again, if I setup a CoinJoin Coordinator for Wasabi users with a bit of tweaking it's not impossible. Getting people to use it would be the issue. But if I am charging no fees I can see where every TX came from and where they went.
How would you be able to see where every tx came from or where they went? Did you read gmaxwell's explanation about Chaumian blind signatures?
Don't the users learn which inputs match up to which outputs?
In the simplest possible implementation where users meet up on IRC over tor or the like, yes they do. The next simplest implementation is where the users send their input and output information to some meeting point server, and the server creates the transaction and asks people to sign it. The server learns the mapping, but no one else does, and the server still can't steal the coins.
More complicated implementations are possible where even the server doesn't learn the mapping.
E.g. Using chaum blind signatures: The users connect and provide inputs (and change addresses) and a cryptographically-blinded version of the address they want their private coins to go to; the server signs the tokens and returns them. The users anonymously reconnect, unblind their output addresses, and return them to the server. The server can see that all the outputs were signed by it and so all the outputs had to come from valid participants. Later people reconnect and sign.
1) Because all the other coins in the coinjoin would be that persons. That is the point.
is the problem. It's usually (not always) not later, it's then and there. a->b->c tend to happen in somewhat real time. So now I know what to look for. And with blocks being full with ordinals at the moment you can probably eliminate 80+% of the TX, take out what are other known addresses and transactions. And the few dozen or hundred at the most can be sorted through at the governments leisure.