Well I can tell you this much, expect it to be based on the Fusion platform, with it being longer and slightly wider. The Attribute mule is already running around as seen here (its a mash up of the MKZ and Fusion for the upcoming MKS, the Lincoln version of the Taurus)

The new Fusion platform should take care of the interior issues with the current car and the next gen Taurus should loose a decent amount of weight because of this.
As for power increases...well I wouldn't be so sure about that. Going forward manufactures are going to have to meet a fleet avg of 34 MPG in 2016 and 54 MPG by 2025. All the rumors about the next gen Mustang have me believing that we won't see a firebreathing GT500 any more, but a NA 5L in a lighter package in the form of the GT350 that is a better all around performer then the GT500 was.
I'm assuming we'll see a Fusion ST with the new 2.3L Ecoboost I4 from the Mustang in it (with about 300HP or so), so we might not even see a SHO next go around...Ford is going to have to figure out where it wants to go with both cars and how to keep them separated.