So far people are commenting primarily on American litigation and regulatory fines. However VW will be more concerned with multiple international regulatory fines in Europe, South America, South Africa, Indonesia, Australia....... Big company, very big immediate problem.

The fallout is reputational damage, and more of an unknown. Like has been said already, I personally think many firms could conceivably write software that could work this way, and we simply don't know yet if this is the case, but surely all VAG firms could be at fault with so much shared technology and processes?
Not a good day to be a VW/VAG owner! Still wouldn't want a Toyota of any description, unless a Lexus LFA perhaps, lol!