We all have been caught up in "White and Black" since season 1 - Backgammon, the stones, eye colors, etc - and ever since The Incident many, including myself, have been placing MIB in the "black" side, for obvious clothing reasons, and then placed Jacob on the "white" side. But in almost every scene I can think of, Jacob was wearing black and white. A white shirt, sometimes with a black jacket, or on the island even this week he is wearing worn black pants. There is also the argument of the freewill vs. destiny, and with Jacob it always seems to fall in the middle. He might give a push or a bit of inspiration, but he always reminds one that they have a choice. He repeats this in The Lighthouse with Jack. So I have a few thoughts on this, and bear with my ADD here.
The Concept of three- The yin and yang for instance. It represents 3. One white, one black, but then the central meaning is that with the two you have the third, composed by combining both equally (with a cool sin curve to it...but I won't go into my thoughts on that here). Many have suggested that there are really three entities on the island; one more that we haven't seen yet, and I am one of those. I kind of look at it as three steps toward "enlightenment" or something. MIB on the bottom, but I didn't know if "white" would be the second, like the yin yang, or it would be the top, because it is pure. In this theory there may be candidates for each...i duno, but I do believe this is the case with at least MIB and Jacob. MIB wants a replacement so he can leave, so as not to upset the balance. Jacob, if he is the benevolent force...i don't know if he would want to leave for a reason like getting bored, but there would be some purpose. Sawyer will play the long con on MIB, so i expect him to look like the bad guy again, he likes doing that, even though he is good inside. He might become the new MIB, but as a sacrifice.
Another thought... The flash-sideways. I believe this is an example of what MIB said at the beginning of the incident. They come, they destroy. Time is going round and round, or at least the same thing/game is, and MIB is tired of it. In this timeline events played out in the way that MIB predicted.