A good point was made above about there being a clue to Malcolm doing it. Malcolm said he had a deal with Oliver, and at first I thought the deal was oliver would make him Ra's in return for helping him beat the old ras, but due to time constraints Malcolm didn't really help all that much. It makes much more sense that the deal was that he would bring back Sara.
A good point was also made above at how this kind of makes Laurels story in season 3 pointless.
As a side note, I hope that if it is done by Malcolm, team arrow stops hating him. Their hatred of him is kind of redundant at this point.