Like say they get to season 7 or 8, they want to freshen things up a bit, jump ahead 10 years or so where Carl is around 30 and his sibling is around 16, and you follow the next generation of survivors. It'd be interesting to see how Carl would try to live up to his father (who would of course be given a suitably heroic death), and explore what it's like having been born in a zombie world having known nothing of what life used to be like.
At this point we have no idea what the baby will be like when it is born. If everyone is already infected, what effect will that have on a next generation of babies?
I'm not talking biologically, just about what their attitude is. At the moment the adults remember life before zombies, so they're clinging on and hoping to rebuild civilisation one day, but Rick and Lori's child won't remember anything like that. I just think it'd be interesting to see the zombie world from the point of view of someone who sees it as 'normal'.