I received a very good, detailed, and intelligent response on the Tesla forum (not to be confused with the Tesla Motor Club's Forum) about the Roadster.
I think the point is that the Roadster was originally built using completely different techniques, strategy, philosophy, and tactics. They got it to work, but the learning process simply taught them to do things differently in the future. So they have. The Model S, Model X, and even the upcoming Model ☰ are all larger platforms. There is more space and volume to work with to conceal, hide, stash, or put away an accessory devices that are needed to make those vehicles work better than was possible with the Roadster. The exercise at hand was to increase the overall range of the Roadster by replacing the battery pack with a version that uses never, higher capacity battery cells. That's it. Tesla made that rather plain well over two years ago. From the very outset they were asked whether the new battery pack would be Supercharger capable and they gave a firm "No." as an answer. The cooling systems and DC Fast Charging hardware simply has nowhere to go in the car, and even moving to the battery management system would require redesigning the whole car again. That's why Tesla had instead considered releasing a completely new spiritual successor to the Roadster around 2019 or so. They learned from their exercise with the Roadster, smart EV, RAV4 EV, and B250e that building an electric car out of an existing platform is far more trouble than it is worth, and it is far better to start with a new project from the ground up. It is highly unlikely that there will EVER be a Supercharger compatible upgrade to the original Tesla Roadster. And if there was to be something like a Model R or Model Z, those have been postponed indefinitely due to the need to release Model ☰ and Model Y, and any new pickup truck products first.