I think we need to distinguish between *configuration* priority and *manufacturing* priority. Tesla is not going to reconfigure its manufacturing lines 7 x 4 (PXXD, XXD, xxD, xx) = 28 different times -- that is much, much more expensive to them (in terms of cost and downtime) than the difference in delivering to the east coast vs. west coast. Historically, this is the approach that Tesla has taken with the Model S and Model X, and I see no reason why this would be different with the Model 3.
Now, is it possible that Tesla will open up the Model 3 *configurator* for reservation-holders in a given macro-region (e.g. US + Canada) in the provided sequence? Sure, let's say they do that. Months after that happens, when production's about to fire up, Tesla will have a good idea of *how many* people have actually ordered (vs. deferred or cancelled), and *what* they ordered, they will come up with a manufacturing plan to drain that sequence in a way that maximizes their profit and delivery numbers. To me, this means that they will (as Elon has stated explicitly) deliver PXXDs first (likely in the same 1-7 sequence that the rep gave), then XXDs (again, likely in 1-7 order), then xxD (1-7) and xx (1-7). This approach makes good business sense for Tesla, as they will make better margins on the PXXDs (very important since the Gigafactory will not be up to full speed yet), and they will also only need to reconfigure their Model 3 manufacturing lines four times (instead of 28).
To spell it out explicitly, under this rollout plan, if you're a non-owner on the East Coast and order a PXXD, only the following six groups will get their car before you:
1. West Coast family members and employees who ordered a PXXD
2. West Coast existing Tesla owners who ordered a PXXD
3. West Coast non- Tesla owners who ordered a PXXD
4. Central US Tesla owners who ordered a PXXD
5. Central US non-Tesla owners who ordered a PXXD
6. East Coast Tesla owners who ordered a PXXD
Right after that, you're up:
7. East Coast non-Tesla owners who ordered a PXXD
...and then:
8. West Coast family members and employees who ordered a XXD
9. West Coast existing Tesla owners who ordered a XXD
10. West Coast non- Tesla owners who ordered a XXD
...etc...
28. East Coast non-Tesla owners who ordered a xx (base model)