The harder parts of machine-piloting involve interpreting the world (lane-finding in the absence of striping; distinguishing hard obstacles from ephemeral objects like paper, leaves, weather, reflections, and so on); and participating in a social environment (what driving postures indicate what intents? What do the local humans consider rude or polite? What are they expecting?)
(A truly advanced autopilot would seem almost magical to a human— it would be able to back-solve diffuse and specular reflections in the environment, and accurately deduce the presence of oncoming cars around corners that would be totally invisible to a human driver. It could predict accidents several seconds before they begin to play out, and the sudden braking/maneuvering in the absence of any visible threat would seem strange and confusing to the humans inside).
Tesla is nowhere near cracking these things; they're still on the ground floor. I still predict that current pre-buyers of so-called "full self-driving" are not going to get what they were promised, and going back on that will probably be bad both for Tesla's reputation and their wallet. If I had to guess, I'd say that if Tesla delivers on Level 5, it will be with a hardware platform that doesn't exist yet, and a software platform that is close to "complete re-write".
As it stands, their misleading marketing on self-driving capability is both dangerous and borderline fraudulent.
All that being said, I'm long on self-driving as a technology; just short on Tesla's current approach to it. It's a shame because I suspect both Waymo and Cruise are doing significantly better technologically, but I trust in their ability to execute a product significantly less. I'm not sure who will actually crack it.