Right, because the dynamics of a solid axle RWD car are exactly the same as the FWD independant suspension Fusion.
Think about this, when you load up the car in the corner, the lateral loads compress the rubber in the subframe bushings. This causes the subframe to shift relative to the body. The orignal engineers tune this and the other bushings so that the shift of the subframe is integrated with the other compliances in the suspension. If you start tying the rear and front together, you will alter the way the subframes shift, probably causing them to twist, rather than shift. This will find it's way back to the wheel, resulting in toe-changes that could reduce the steering feel, alter the balance and introduce unprefictability.
It could turn out to be better though, so I say try it out. But I just want to point out that there's a lot more to suspension tuning then people often realize.
And not all cars use isolated subframes, though it is becoming the only way to meet the NVH requirements of the market. I remember reading that the Accord uses isolated subframes on the I4 models, but not the V6, or it could be the other way around. The Ford 500 uses an isolated rear subframe on AWD models but not FWD.