I love Luke and Kenny but I don't feel as if they are going to make that decision because they're to lazy to make a whole new story for a determinate character in season 3. Now a save Mike or save Bonnie decision would be a lot more challenging to decide and make more sense.
In the opening scene in episode 5 Clem immediately turns around because of the gunshots. The game goes into slow-mo and either has you kill the Russian that is pointing his gun at Mike or Bonnie, to save one of their life's.
Near the end or halfway through they would probably kill of whoever you saved knowing telltale. But I think it would be more interesting and predictable choice than a Kenny or Luke decision.