[FenwickHockey65]

It's a double edged sword. Reveal it ahead of time and you generate interest and anticipation. You also lose sales on your current model and your competition gets to work on improving their product, plus less-informed customers go to dealerships only to be disappointed that what they want is still months away. If you reveal it right before production you miss out on all the buzz (unless you generate some yourself) but your customers can buy right away.