The short answer is there would have been an expansion of the green levy. It would have resulted in an increase in tax. This is consistent with what the United States did with the American version of the green levy, which is referred to as the gas guzzler tax.
When the vehicle consumption testing requirements in the United States moved from a two-cycle test to a five-cycle test, the gas guzzler tax in the United States continued to be determined by reference to the two-cycle test. In this case it is proposed that the green levy continue to be determined by reference to the two-cycle test, so there won't be an expansion; there won't be an increase in tax.