Very few options for a set that size, but here are some of my thoughts on it:
1. It is from the OT or PT. They would not green light such a huge set before TFA is released and they can see how much screen time it gets, fan reactions, etc.
2. If it is a play set, the price leaves very few options. The Death Star, Echo Base, and the Ewok Village already exist/will exist. That really just leaves Cloud City and the Yavin IV Base as options.
3. It is not a Death Star. Too soon after 10188 has been on the shelves, especially if they are producing more 10188.
4. Given the price/size, if it is a vehicle, it is an exceptionally well-known one, and so there are only two options: Star Destroyer or Millennium Falcon.
I am hoping for (and would put my money on) a Star Destroyer or Millennium Falcon. Both 10030 and 10179 sold well, were very popular, and have a lot of fans asking for newer versions. TLG has released newer versions of previous UCS sets (see X-wing). It has been five years since 10179 was discontinued and seven years since 10030 was discontinued, so they've waited a respectable amount of time. Moreover, there is a clear way for them to distinguish both new models from what existed previously: interiors. They have been trending in this direction with UCS sets lately. I have seen a number of 10179 mods with custom interiors, and they could easily put a bridge mockup in the body of a star destroyer (a la 10221, maybe with a few other rooms too).
So... small chance it's a big Yavin IV/Cloud City playset, but most likely, in my opinion, it's going to be a redesigned UCS Millenium Falcon or Imperial Star Destroyer, with interior.