Crazy thought, but could Starkiller base actually be a super-weapon hidden inside an entire planet?
In this shot from the trailer it looks like the ground is opening up. And on the poster we see a Death Star type of super-weapon that looks like a snowy planet with a slit/crevice in the middle.
EDIT:
Maybe this shot is inside Starkiller base. Maybe it's the internal reactor or something, perhaps even the inside of that big red "lens" or whatever you'd call it, that we see on the poster. Otherwise why would space be red? Also it would explain that building in the bottom right of the picture.
2nd EDIT:
Yes, apparently it is a planet sized super-weapon.
http://www.starwars.com/databank/starkiller-base