Well, here we go! Elon Musk just revealed that the D is for Dual motors. Unlike AWD (all wheel drive) cars, Tesla's dual motors will function independently for max power, efficiency and/or range, depending on your use of the accelerator and settings. The two motors will increase the max speed of the P85+ from 4.2 seconds 0-60 to 3.2 seconds! Use of dual motors will also add to the efficiency of the batteries and therefore increase the range.
The Other: A is for autopilot. Model Ss will now have the ability to almost self-drive. Elon Musk said you cannot go to sleep and arrive at your destination, but rather the car will work to make sure you stay in your lane at a proper speed so you do not hit or get hit by anyone. There will be sensors surrounding the car watching for both hard and soft objects; these sensors will provide updated output on your instrument panel showing what is around you (I believe he called it "active safety.") You will get tactile feedback from the steering wheel, and the car will brake if it senses trouble.
But wait! There's more: the car will be able to self park. You can get out of the car, and it will park itself. Similarly, it will come to you. If you have set some appointment in your calendar, the car will pull out at the designated time, with your music loaded and the car in a heated or cooled state, depending on the season.
It really is incredible! Can I change my order, please?