Though the image below is particularly grainy - and no intelligence service-level image enhancement is going to change that - there are a couple of relevant pieces of information we can draw from it and collate with other items of data that have come our way.
On the left we can see a vertical structure, made of Technic elements, with a minifig in a First Officer uniform to its right on what appears to be an elevator platform giving access to the bipedal structure next to it. This is the AT-ST and it clearly has no cockpit head sitting on its swivel waist and legs. At its feet is a pair of minifigs - one is obviously Captain Phasma while the other is also a First Officer-type minifig.
Based on the unofficial set description:
Help Finn, Rose and BB-8 to capture the unfinished AT-ST!
Jump to the suspended lift and climb onto the walker. Turn the steering wheel to deploy the gun, and control the walking pylons to start moving. Lead fire to retreat to a safe place where you can hold out until reinforcements arrive!
Can Captain Phasma stop our heroes before they manage to escape? Their fate is in your hands!
it is easy to spot that the minifigs included are Finn and Rose in their First Order disguise, Captain Phasma and BB-8.
Earlier posts on Rebelscum had reported on the Finn and Rose figures but weren't able to attach them to a particular set, until now.
With a cloak of mystery surrounding this set, the scene that this is based on must be particularly important.