I don't think there needs to be a content filter so long as the messages from your opponent can be hidden. ACR has a good system where player comments are in a certain tab along with a report of who won the previous few
hands. Since the tab isn't all too useful to the players, hardly anyone types or reads chat unless it's a home game or a break.
To be frank, poker is adult oriented. If an adult can be so offended by a comment that he or she changes his or her style of play, the responsibility should fall on them and not the poker room.