Today's Super Smash Bros Pic of the Day showcases a new stage for the 3DS version. The stage is set in Lumiose City from Pokemon XY, and seems to take place at night. As we know from Smashville, it is possible for stages to change depending on the time of day. The Lumiose City stage might change with the system clock too, since it does in Pokemon XY.
According to Sakurai, "Up until a few seconds ago, the fighters were brawling on top of that tower." "That tower" is referring to the Prism Tower in Lumiose City, which is also the Gym. This stage is likely going to be similar to Delfino Plaza, and have the fighters fly around Lumiose City on a platform. The five plazas down below are light up, and seem to be the only other attention grabbing parts of the stage. Maybe the fighters will go around the five plazas before the ride goes back to the top of the Gym.
For reference, here is a picture of the Prism Tower in Pokemon XY: