First, keep in mind that the move from 200 to 400 per week is actually pretty binary and quick. It's being done by onboarding a 2nd shift of factory personnel. They've been training for the past few weeks and presumably have some start date designated for them. Then it's simply a matter of picking up production, and given that there are no known parts delays or other outside factors, they should be able to just start at close to 200 per week from day one. That will nearly instantly double production, as silly as that may seem.
Anyways, take a look at my estimated production plan: Production Rate (incl manufacturing waves) - Page 27
I'm thinking they can make it to GP2000 by the end of the year. So, (8781-2000)/400 = ~17 weeks. However, you do have to factor in a large number of cancellations before you. There were around 1600 in Q3 of this year, mainly due to them contacting reservation holders that couldn't commit to the vehicle. That's nearly 4 weeks you're moved up! That moves you from late April to late March. Factor in additional cancellations as more people were contacted in Q4 ahead of you, I don't think March is totally out of the question.
Nonetheless, I would manage expectations and tell your friends and family April for the time being. Things can happen, so I wouldn't follow the best case scenario. If that were true, I would have had my car 2 months ago
Has anyone tracked the total cancellations so far? I've heard a number as high as 4,000.