Open, unregulated chat is a nightmare. Bullying, bribing, and all sorts of other problems when deep (in game) chat systems are used for other purposes. Not to mention language barriers... Hopefully association chat is and can remain problem free.

Alternative suggestion:
Allow users to send one of a pre-defined set of messages in certain occasions. So (before a game) we could "taunt" or "encourage" with kid-friendly, approved language. After game send a "good effort" or "poor sport" message, etc.

But with the "chat" so nerfed as to be appropriate, I doubt it would add much to the experience.