Based on this and other threads, it appears the likely causes of front vibration in the AWD Model S's are:
- uneven drive shaft lengths
- too sharp drive shaft universal joint angles
If that is true I would think one solution would be drive shafts with tighter universal joint bearing tolerances.
Short of that moving the differential to the center of the car may help :|.
My 2017 Model S 75 obviously has no front motor. I wonder if the rear shafts are the same length, even the same part numbers?
When I was deciding on the 75 verses the 75D, I specifically choose RWD because of the front motor noise (not vibration), just didn't like having that sound in front. Other reasons included only a 0.1 second 0-60 time difference, a lighter more nimble front end, a several hundred pound weight reduction, dislike of torque steer, and no real benefit from AWD (winter tires do 95% of the snow traction needs).
I would very much like to get a Plaid eventually, but not until this front vibration issue is resolved.