I think the biggest obstacle in finding a solution is we let the outer 10% dictate what the policy will be. On the Right, you have the "never for any reason crowd" and on the Left you have "no restrictions ever crowd". As long as these are the people trying to shape the policy, it will never get done.
I say we make the fringes unhappy (we really should make the fringes unhappy a lot more than we do) and do something most people can get behind which would be a 16-20 week limit, after which it would need to be for the life/physical health of the mother.