The downside of doing so is that it still gives plenty of time to cancel the changes at year 12 or 16, once it becomes apparent who will stand to benefit/lose from the change. This type of hacking future benefits is evidence in many of the tax overhauls, which use predicted future savings to offset short-term costs. And often those future savings are legislated away before they come to fruition.
(Of course, sometimes those future savings wouldn't have happened anyways, due to unreasonably optimistic assumptions about the performance of the economy.)