i'm not going to say there aren't bad feelings but there's a bit more too it because Roger played the Hopman Cup once with Hingis when he was much younger and another time with Mirka. he clearly moved away from it and even Davis Cup since he became the dominant player on tour. Patty loves the Gold Coast tournament as well and has played it for the last 8 years or something.
It's not the type of tournament players want to play every year either because you have to be there for news years etc.
It's always been something i'd love to see though - my two favourites players in mixed doubles together. not likely to ever happen though