Yes, this has definitely been on my mind as well. Any vehicle with 20 year old port injected based engine technology is definitely not going to be as flexible from an emission turning standpoint as the modern direct injection engines. These are the engines that companies like Porsche have in their arsenal.
Another possibility is that the exhaust valving needed be adjusted to meet CARB's sound requirements, which are quite strict from my understanding. That being said, we still don't really have any valid information on the situation right now, so this is all speculation...