Based on this season and the votd raid. I think the seasons this year will be centered around the witness and potential heralds, zealots, and disciplines. The raid had rhulk the first disciple, this season had calus herald of the witness, and I think this coming season will be centered around Eramis getting freed from her stasis prison by house of salvation survivors while variks or Mithrax warns us of their plot. With potentially Eramis becoming a zealot of the witness.
The last season of this year could revolve around savathun being revived or xivu arath finally getting revealed or the witness arriving to our system finally.
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I'm thinking next season is about Rasputin and Mithrax and the season after will be about either Eramis or a rebooted Clovis become the next Disciple. It would be cool if Clovis raised a darkness Exo army to fight us and they'd be all ripped up with circuts and wires showing and while making "glitchy" wailing sounds with missing an arm moving about like Zombies. I know this wouldn't be possible for seasonal content but one can dream.