Note that the front cross over section on several of those cars has been modified or even removed. That isn't the sort of mod a manufacture could accept without some real consideration. The movement of the radiators into the crush area isn't likely a big deal but it does suggest that the car probably wouldn't meet a 5mph impact test. It appears the hood needs to be modified to clear the front of the motor. Did they have to modify the sumps to clear the suspension subframe? None of those look like a plug and play change like say swapping a V8 into the engine bay of a BMW 530.

While it's great that a motor can produce so much more power than it could stock, ultimately most people don't care, even most buyers of these cars (original new owners) don't care. The VQ isn't exactly a week motor and in 3L form it was a great motor. The I6 may also be great and it might be capable of silly high power but still, the V6 seemed to make more sense.