Giratina goes back to the Distortion World
Giratina is scheduled to leave raids on 11/20 at 1:00 PST, which is a bit over 28 hours away as I post this. What's next? Idle speculation welcome. We'll probably get the official announcement within the next 5 hours, so guess now before it's not a guess at all.
My guess is Groudon for 3-7 days, with a shiny, followed by Palkia.
Answers
I'm hoping for an announcement from Niantic at 1 PM PST, or in 45 minutes. Fingers crossed for something that isn't garbage.
Worst case scenario: Origin Forme Giratina with exactly the same moveset as Altered Forme.
Even worse case scenario: Registeel with shiny.
And oh, do we expect Groudon as our new December Special Research Breakthrough, the first of the Gen3 Legendaries? If so, less chance of getting a shiny now (but not non-zero).
The Weather Trio won't be Research rewards. They didn't do it with Lugia and Ho-Oh or Mewtwo, their equivalent in previous gens.
They'll probably do Lati@s next (or Delibird to tie in with Christmas?), then maybe the Regis again (shinies!), with randoms in between each, like Confusion Exeggutor or Kingler with Crabhammer.
I'd guess either Dialga or Palkia will come next. Unless my memory is wrong I don't think trios have had their main rotations broken up, not counting raid days and 48 hour events. The birds were released back to back, the beasts were back to back, the weather trio was back to back, and the Regis were back to back. Mini events and re-releases happened either in between sets of trios or alongside one of the trio bosses without completely removing it.
I've had another thought on this - what will the Special Research Breakthrough for December be? If they follow the old trend, we should expect to see Groudon, because it has always been 3 legendaries(birds), 1 bookend (BS Snorlax), three legendaries(beasts), 1 bookend (Shedinja). Sounds like Groudon is next. Hope that's the case, but if so, it would be a little silly to give us 3-5 raid days of Groudon now before Palkia.
Switching my guess to Palkia.