Front wheel drive vehicles are more fuel efficient than rear wheel drive vehicles. This is evident in the increased mileage of the new Tesla S all wheel drive versions where at highway speeds the front wheels are mostly powered allowing for greater energy savings and longer range. The all wheel drive version of the S85 is 7.5% more efficient than the normal version. Since it is probably just as cheap for Tesla to mount the motor in the front as it is in the back I believe they may go this route to increase efficiency for the low cost model 3 and offer all wheel drive as an option. I would assume they would go with something like 150hp standard in the front with an optional rear motor of 150hp or 300hp for the performance version of the Model 3. A 7.5% smaller battery pack is a large savings when it comes to keeping costs below $35000 for the base model. .