When my car is ready the end of March I will be making sure that I have a D pack battery or I will be refusing deliver.
I have flashbacks to a conversation I had very early on in this forum. I was concerned that Tesla might try to screw me, after all, that's what every other car manufacturer does. Bonnie (the wonderful woman that she is, and no she didn't pay me for this) encouraged me by telling me stories about her service experience with Tesla on her Roadster. In the 15 months I've gotten the car, I can say that I certainly understand why she raved the way she did about the experience. Now it's my time to pay it forward: Tesla has always been very straightforward with me, even if communications challenges have been somewhat frustrating.
You are highly likely to get a "D" pack, given that your car will be brand new. So there's a .0001% chance you should be worried.
However, even if today you were to get a rev. B pack, I can assure you that Tesla would stand behind you with the same service experience, and that you would get everything that is promised to you the day you purchased your car.
You would have an argument if your car were built with a refurbished "A" pack, but the chances of that are nil or better, considering that no one has reported a "B" pack replacement with "A", and the highest known VIN with pack "A" is < 10,000.
I will only suggest that you not overly stress yourself. Don't worry yourself about "deal-breakers" or stuff like that, you'll just be stressing yourself. Just trust the fact that 99% of current owners would buy their car again, by far the best car surveyed. #2 is the Porsche Boxter at 95%, #3 is a tie between Volts and 911's at 91%.
Don't worry, it'll help your stress level... I promise.