The ship in the background could just be completely random. It has a striking resemblance to the Frigates in the halo series, for instance the Forward unto Dawn. If Bungie is going with that same kind of aesthetic for the ships, that could mean that that ship is human. Maybe guardians ships will play a bigger role, who knows. But then on the flip side it could likely be a fallen ship of some sort, because it kind of has that long back part that skiffs have. Also notice how it is not really moving, like there is no motion blur or anything to suggest that it is moving, which could mean it is a drop ship of some degree, which is exactly what skiffs are. The location that they are in could be the last city, if the cabal actually attacked it. It was hinted that the cabal do attack in a toy that showed up on amazon hinting at it. It does look dry and arid, and maybe it is the last city many years after some kind of full scale invasion, that decimated the city. Or maybe it is a completely different part of the earth. In the time between destiny 1 and destiny 2 the traveler could of been fixed or it could of fixed itself, and moved to a different part of the globe during the cabal invasion to save itself. On the flip side of that, and this is my personal theory, is that this poster is on mars. The architecture matches up with the building and things found in the Psion flare mission on the very top of the building. Also the cabal are supposed to be the main antagonists. The traveler being there could mean that it has moved back to mars, or it just shows up in the background for marketing. That brings me back to my finale statement, and it has to do with that ship again. If this picture is on mars, which i am inclined to believe, than that ship could be a cabal ship. It has the same very blocky look to it, like other cabal drop ships, and it would make more sense than it being a human or fallen ship. Phew, that was a lot of typing.