The usual Call of Duty cycle goes from Infinity Ward to Treyarch and then Sledgehammer Games before it begins anew. Activision Blizzard has broken tradition in the past for a good reason.
Having said that, it's safe to assume that Treyarch will spearhead the next Call of Duty game.
Here's what Hope said in a follow-up tweet about the next Call of Duty game: Activision wont make a final decision for another 12-18 months & what Microsoft chooses to do is up in the air still assuming the deal goes through. Ultimately Treyarch is working off the assumption of 2 years. Things can change so keep that in mind with this. In case you're wondering, the leaker is talking about the unified engine that future Call of Duty games will use, starting with Modern Warfare 2. But, while Hope is a reputable leaker, his recent claim stands in contrast to what Tom Henderson said earlier this year. Henderson also reported that Treyarch is working on a free-to-play title for next year. Even if Treyarch and the rest of Activision Blizzard can handle so many projects at once, you can't help but wonder which of these rumors is true or not.