L5 autonomy is a absolutely a long way off (if ever practially acheivable) and Elon is a bullshit artist, but I don't understand your comparison to the halting problem. Could you elaborate?

I interperate your comparison to the halting problem to mean that even if we ignore the feasability of a particular solution, it is literally an impossible problem to solve.

My understanding of L5 is driving without external human intervention. In one sense we already have the technology to do that - our brians. It would never be feasible (or ethical), but if we could put a human brain inside every tesla, wouldn't that achieve L5?