Should conferences do early rejection?
I'm in the health and social sciences and I have never attended a conference that has used this format for submissions. This seems like a lot more work for conference abstract reviewers and program committees (all who are volunteers). 

I have seen a movement towards "late breakers," where you can submit an abstract for a subsequent round of reviews, often after the initial acceptance/rejection notifications are distributed. You typically are not able to re-submit a rejected abstract, but could potentially revise or (ideally) propose a different project for the conference. I guess there are pros and cons of each approach.