I agree with your assertion that the tax credit will matter more to the "average Model 3 buyer" than to the "average Model X/S buyer" but you're missing something on delaying the 200k and starting the tax credit phase out:
The further it's put off, the higher production will be and the more Model 3 buyers who will be eligible for it while it is available. They aren't slowing production at all, they're simply moving some of it to Canada to ensure the phase out isn't triggered until the 3rd quarter this year. At 5000 cars/week down the road that's nearly 60000 that will be able to get the full credit over the much lower number per quarter that would now. Now go back to our assumption that the Model 3 buyers will be more affected by the tax credit: You will see a higher order rate and almost certainly higher optioning of cars later in the year with the full tax credit available longer. Good for Tesla, good for its customers. Same number of cars produced.
As stated earlier, I'm a pre-reveal, in line at 10AM, linestander 40 miles from the factory. I haven't gotten my invite yet, as many other haven't either. Saying Tesla is running out of people to order at this point simply isn't accurate.