I understand the theory and thought of it myself already, but I just don't see why parental controls could not be the way to handle these situations.
If a parent is so concerned over the language that is to be spoken over voice chat then maybe they wouldn't have bout them that game in the first place or would have set parental controls to block certain aspects of certain games based on the games rating without a parental unlock code.
but.... OTOH, I think an individual earpiece is probably the better way to go anyway. But can you do 4 individual earpieces for 4 player local online multi?
But in the future, a Wiispeak device that also work with a wireless earpiece (like cell phone speaker and bluetooth earpiece) would be the best route to take. WiiSpeak out of the box and wireless earpiece optional add-on, but that's just another idea for the Wii2 thread.