I suppose if it were found legal for Obama to ban guns by decree, then it could be found legal for a future president to ban abortion in the same way.
Has it been found legal?
I don't think any president as yet anyway has the power to ban either guns or abortions by presidential decree. Maybe as Congress becomes more and more dysfunctional, as the people of this nation become more and more complacent, the president's power could grow to that point.
but, it's not there yet, despite the recent increase in executive orders.
Maybe an attempt to ban guns and/or abortions would be a wake up call to actually get involved in this government of, by, and for the people.
Or not.