A couple of months ago I initiated a chargeback with Bank of America for this reason. The value of the stay was ~1500€; so the chargeback amount was around $42 (the amount I was overcharged due to their use of DCC).
I won the case, and received my $42 back. AirBnB sent me some automated email asking why I did a chargeback. I clicked the "other" box. I never heard from them again.
I've since made another booking, and am preparing to file another chargeback for the same reason.
If we all do this, Visa / MC might eventually force them into compliance.