Reversing the decision on SSM will require and amendment at this point. That isn't going to happen.
Repealing ACA is possible, but I'll bet it won't.
An amendment will likely happen due to the countries shift to the right and the votes will be there within 8 years. As for the ACA all we need is a GOP president and now Hilary will have to defend the ACA and she will lose votes due to that and with the shift to the right I predict a GOP President, which is all that is required to repeal Obamacare.
What country's shift to the right?
I thought this thread was about the U.S. where the majority of people now support marriage equality.