I disagree with everyone here dissing the OPs idea. I think he is correct (but I don't think Tesla should do this - I'll get to why later) it could be done and that there should be an option kind of like the "cheapo" option. Imagine it right at this point in time: Tesla comes out with the news tomorrow that they still have the $76k Model S 70D but starting tomorrow there will also be the $49,999 Model S 70D"*
Notice the "*"? It means:
*The car comes without a charge port. The battery of the car is owned by Tesla, you will own the car. You will only be able to refill range by visiting one of our BatterySwap stations. Each swap will cost a set amount of dollars, in accordance with your SwapRate agreement that was agreed upon purchasing the car. As the battery belongs to Tesla you will agree to plug the car in to the electric grid in accordance with your PlugMeIn agreement, or face economic sanctions as per the contract. Using 3rd party batteries is forbidden - You will agree upon Tesla having the right to reposess the car should you remove the TeslaPack.
Now this would get a whole other type of people in to the game - people who normallly couldn't dream of buying a Tesla. They would stay in agreement with the PlugMeIn agreement since they wouldn't afford getting penalty payments for not being plugged in enough (remember these are people who stretched to buy a Tesla). This gives Tesla access to a virtual giant battery for a large part of the day and night, that they own. This would be making Tesla the world leader in distributed load balancing services. Tesla can basically say to the utilities: "You want to rent a 50GWh battery (bit arbitrary number but in the ballpark) from us every night"? How much is this worth? Ballpark answer: ALOT.
I still think they shouldn't do it 'cause it's not just the classy thing to do.