They are going to have to come up with a way to do it via mobile or they are going to have a lot of pretty annoyed customers. My mother got her car on May 2018 and purchased full self-driving. It's a 7 hour drive one way to the nearest service center. The text when she - and I - bought it for our respective Model 3's indicated that all that was needed was validation and regulatory approval. There was no mention of hardware upgrades - the text on the car said it the hardware to enable full-self driving was already installed - or the need to find another reason to visit a service center, or anything about service centers at all. I guess we'll see but so far the roll-out plan is pretty opaque.