Now that I can agree with. It needs to be implemented in the future so nobody knows who the POTUS would be when it's enacted.
But back to the point; There will likely be 2 vacancies (at least) this upcoming 4 years. Roe is in jeopardy with Romney in the White House.
There's no indication that Romney would base his Supreme Court appointments on abortion. In fact, that's not what he did as governor of Massachusetts, a history which was challenged in the South Carolina debate by Newt Gingrich:
GINGRICH: Governor Romney did appoint pro-abortion judges.
ROMNEY: I appointed probably 50 or 60 judges--at the trial court level, mostly, the great majority. These were former prosecutors; 80% of them former prosecutors.
We don't have a litmus test for appointing judges--asking them if they're pro-life or not pro-life. These were people going after crimes and the like. I am pro-life. And the Massachusetts Citizens for Life and several other family-oriented groups wrote a letter two weeks ago and said they'd watched my record, that I was an avidly pro-life governor. I am a pro-life governor; I am a pro-life individual. Is there any possibility that I've ever made a mistake in that regard, I didn't see something that I should have seen? Possibly. But you can count on me, as president, to pursue a policy that protects the life of unborn, whether here in this country or overseas. And I'll reverse the policies of this president.
South Carolina 2012 Republican primary debate
What's interesting is that Social Conservatives have thrown an utter hissy fit over the fact that Romney did NOT make activist appointments. And yet, here you are, trying to convince us that he will do just that in the future, despite the fact that he didn't do it when he had the opportunity.
It's completely possible for people to be pro-life and still be able to resist the temptation to legislate from the bench. If you read Romney's full response above, he clearly believes that there were some things within his purview as an executor and other things that weren't. Romney appears to have a very well-ordered mind and the capability of understanding his role in governance and the limits to it.
If you're willing to take an honest look at him, I think what you'll find is that Romney doesn't suffer the illusions of grandeur that cause Obama to blur the lines between the three branches of government. He's not looking for activists. He's looking for people who understand the law as written.