I've got a plan of the ship and some basic tiles planned on paper. I haven't yet programmed anything. The small number of tiles made me think of making 3D models of them with 2D rendered tiles from the top side. 3D is cool, because you can then change lighting, colors/textures and the size of the tiles. It also means I wont finish this in 7 days, but it never was the idea of 7DRL for me.
The biggest problem still is the idea of the game. I have no idea what the player should do. Maybe fix something before the ship goes boom? Battle alien creatures that were attached to the ship while visiting a distant planet? Maybe I should just create the game without content and wander around the ship, trying to think it that way. Or I could just release the game without content, making the player think what the hell he is supposed to do.
Update: Got the idea and it's a good one.