Continuation
Isn't that how PD is supposed to work?  Aren't there supposed to be specific criteria, as there are in DACA?
And even after those who initially may qualify apply, there is further individual consideration of each application.  So, actually, each applicant is considered individually, with a special consideration of safety of the community.  
Right now, I simply don't have time that I would want to dedicate to pursue this, but once I stop working, I will take the time to read more about the various executive orders of other presidents.  Based on the bit of reading that I have done so far, I imagine that I will find that this order is not so extraordinary.  
It seems to me that those in our country who are firmly set against immigration reform are opposing this order to further their own agenda, and not because of any actual constitutional concerns.