I just saw that a few weeks ago Elon Musk tweeted that Tesla’s Full Self-Driving Functionality will be a “full architectural rewrite”, presumably of the code base.
Rewrites are hard. They often seem exciting at the beginning, because of the opportunity to do everything the “right” way, from the ground up. But it usually turns out that recreating existing functionality, built up over years, requires a lot of effort. If the original software took years to write, the rewrite won’t be trivial.
On the other hand, there is a reason Tesla is the most valuable car company in the world, and now one of the most valuable companies in the world, period. Elon Musk is amazing at leading his people to accomplish what would be impossible for most teams.
A rewrite hardly qualifies as impossible. But it’s usually a pretty big effort.