Here is simulation of Kerbol System with N-Body physics.
The main problem with N-body, that Jool system too small. In trailer we saw a bigger Kerbin, so we can expact that Kerbal Systerm will be bigger than in original KSP.
Another avidence of N-body is two planets Rask and Rusk. They are too close for 1-body physics, so I guess we'll be able to fly betwen two center of mass.