I am going to say construction related modular building. Looks like an insulated CONEX / shipping container. There is nothing like that in any of the concept drawings, or on any gondola systems I have ridden.
I am pretty sure they are going to be permanent, probably control room and equipment room. You can see in these two pictures that insulation and an outside wall surface has been added, no reason to do that if they were just for construction purposes. Probably not something you have seen because gondola stations over water are not common. The other stations have small structures connected to them, but since they are on the ground they are cinder block or concrete structures.