Although I don't think such an attack is practical, as ranochigo has pointed out, I also don't think that such an attack would necessarily be a bad thing. If we reached the point where the vast majority of bitcoin in circulation are "tainted" in one way or another, then the exchanges which are coming up with these arbitrary rules would be forced to either drop them or go out of business, and the only exchanges left would be ones which don't push some ridiculous narrative that one bitcoin is not equal to another bitcoin.

And even without such an attack, I think we are getting to this point more quickly than ever. As exchanges implement more and more invasive KYC requirements (such as requiring KYC for your own wallet), then more and more users are turning to privacy improving services such as mixers and coinjoins, which inevitably end up mixing clean coins and tainted coins together and making the exchanges' analyses moot.