So my point still stands today;
having an "exploitable" keyword/trainer phrase system would be no worse than the current state of global chat.
But if people seriously do care about that, then just make it so you can't create your own/see other people's trainer phrases unless you claim to be "at least 13 (or 18) years old". If that'd be too hard to implement for accounts that are already made, it could just be a toggled option in the game settings.
That way if you're subjected to "questionable content", it's your own damn fault and you can't complain.