Haven't we seen art that basically guarantees Ajani will be in Rivals, presumably giving him the G/W slot as far as planeswalkers go? As psyched as I am that Angrath exists, I don't see him beating out Ajani and Bolas' associate (who I'm guessing is a planeswalker in one or more of the grixis colors) for one of the 2 spots. It seems more likely that Angrath will get the same treatment as Ugin did in Battle block, where he appears in the story, but isn't important enough to justify a card.
I don’t think Bolas’s mystery associate is getting a card for Ixalan. It’s either Tezzeret, who already has a card in standard, or Ral Zarek, who will get a new one with the inevitable Return to Return to Ravnica fall next year.
The packaging leak was a good hint, but remember it also shows Huatli’s planeswalker art for set 2. It might be art for the big expensive statue used on the packaging test.