I'm aware that there have been attempts to simulate the evolution of the Solar System with six giant planets1, as opposed to the traditional four or five. The recent proposed Planet Nine would probably invalidate some of those models, although I don't know how drastic its effects would be.
Would Planet Nine fit into models with six giant planets? Have any simulations been done that support such a scenario?
1 The models I'm most familiar with were created by Nesvorny & Morbidelli (2012).