I wonder what Bungie is going to do with Savathuun and her Lucent Hive. They must still have a part to play. They'd be great allies, if they could stop acting like typical Hive for five minutes and have Savathuun start acting more like a strategist and stop being a deceiver who can't be trusted.
The Cabal and Eliksni have joined us, now all we're missing is a Hive and Vex faction.
Edit: Because Savathuun doesn't have a worm to feed anymore, she doesn't have to follow her nature. She CAN pick a new destiny for herself. Bungie just has to get on top of writing her redemption story.
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Generically speaking, I feel like the story is going in that direction. In the end, all races will be divided in two sides: one sided with the Traveler, the other with the Witness. Probably in the near future Savathun will join us as counter part of Xivu Arath and, maybe, even the Vex.