I don't follow the low end car market outside the US. It's entirely possible that developing countries still have "dumb" cars available, but due to their lack of adherence to US federal safety standards, importing one night as well be impossible for a normal consumer (aka anyone short of Jay Leno).
As far as a cite, here an article that claims 2006 was the tipping point, so even earlier than I remember.
Well, than having a post-2016 car is ruled out then (I am not completely sure about this piece of info though: I will check, there may be exceptions, e.g. vans).
The issue will be about being able to use pre-2016 cars until civilization re-emerges.
They will price those cars out by putting very high taxes on gasoline. If synthetics ever catch up, maybe that's the only way to go forward. Right now, synthetics are like €8/€9 per liter (*) to manufacture, not sure if it's possible to buy them.
(*) According to overheard info from Toyota presenting the technology at the N24 race.