Is Priotity-Pass technically the same thing as Alliance access? I feel that CX might be trying using this new airport policy as an excuse. Even Thai Airways do not mention anything regarding restrcting access for othe *A passangers to its BKK lounges in their lounge access policy.
In any case, I expect there would be amendments to this rule sooner or later as I assume it was not intended to restrict alliance access. I guess there might be other OW/A*/ST airlines without having contracts with local Thai lounges, relying on alliace partner airline lounges.