They won't hire another designer, they said that both films will premier next year, part 2 will be immediate continuation of the same story arc. It would be like a character designer change in the middle of the same season. The are most likely working on both films simultaneously, so another studio was needed. I doubt for a trailer in 2019, as we have nothing - not even a single piece of artwork. I still bet on February, the anniversary of the franchise itself. It is a big date and it fits the time frame.