well he did end up back at tat chasing leia, and in a way he did kill the lars. Just used his troopers to do it. You can only imagine what was going through his mind if the troopers had reported back to him they had tracked the droid to a Lars homestead.I agree that another Vader Obi Wan fight is likely but I doubt Vader will go back to Tatooine again though. His mother died there which he blames himself for and going there would open that wound (but then again Vader is clearly a total masochist as he chose Mustafar to build his Castle on). I'm sure some part of him also blames the Lars family for his mother's death. If he was on Tatooine I would imagine that he would want to kill them which would be slightly problematic for continuity.
My guess it deals with obi learning how to become a blue glowy and vader with at least 1 conversation with qui. A wild question would be will they bring darth maul back into it and retcon his death?