Even without BNG the '19 bikes will sell for more than the '18 bikes. This is because you will be able to sell them next year as the current year bike that is less than 1 year old. Whereas an '18 bike will be considered a last year's bike. So, even without any Alta rebates the '18 bikes will be discounted by dealers, if they have too many of them, and if the '19 are also available to buy at the same time.