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You won't get an official answer detailing when what Tribunals are coming down the pike. They announce the next book about the time they release a book for sale.
This subject has been discussed in the Ars Forum, that they will probably now start revisiting some of the other Tribunals, because they've just now finished covering all of the Tribunals that hadn't had a Tribunal book. Faith and Flame (Provencal) has just been announced for release sometime in June, I believe.