I can’t tell you how many times I’ve read posts on here of people ordering a certain spec’d car only to change it for whatever reason on their own—paint color, tires, interior, model, etc. Really hard to know for sure a buyer won’t change his mind and want something else and they are basing production based on orders and those being filled timely.
It’s not like Tesla is making a ton of these cars in each config and storing them in some warehouse or filling up dealership lots waiting to be sold. They are in limited number based on demand, unlike the traditional manufactures who the press has reported are seeing slow sales and still have 2018 models on their lots. With Tesla sales doing well, if you can’t take delivery of a car when it's ready, it will get sold. Typically you’d have to wait for the next batch to come out of the factory in that config if you changed up or weren’t ready for delivery for whatever reason—business or personal. Something about a bird in hand... Maybe when OP asked about extending delivery time the decision to phase out P3D- hadn’t been made or communicated to the stores’ staff so it was assumed more would be coming out of the factory.
No doubt it’s disappointing to end up not getting the config you wanted. I guess at the moment he could still get it but sure the east coast ones will be sold quickly if not gone already. Glad to hear some of you have been having success.