Nothing is a show stopper, not even cost. You could make an overly priced, low ground clearance, excessively heavy, 100kWh, RAV4 vehicle right now. Dropping cost only removes one of the problems. Model X has an 8 inch ground clearance, a double layer pack as you propose would cut that about in half and leave an unacceptable 4 inch clearance even for average use. Plus the added weight means heavier frame parts and suspension parts so it's an additive effect, which also drives up costs.
Next year Tesla will come out with the Model Y probably using the same pack as the Model 3 so 75-80kWh. Tesla is probably near $120/kWh so that would be a $9,600 pack. Even at $100/kWh they won't suddenly be able to fit a 100kWh pack without improvements in energy density or without significantly compromising the vehicle.