I've always been onboard with Kirkman's word that the story isn't about immunity or finding the cure. However, in the past few years, his word hasn't always been truthful. While a lot of that stemmed from his involvement in the TV show, there has been an occasional deceit in the comics when he wrote responses in letterhacks.

With all that said, that doesn't necessarily mean he's hiding the truth about the end game of the comics. Maybe he is being completely honest and we will never see any sort of cure or immunity arise. But it's much easier to believe these days that there's some sort of story arc regarding a cure or someone being immune that he could be working towards.

I don't believe it will happen but I also don't think it's totally out of the question. If they ever were to introduce an idea that anyone born after the infection is immune from turning, then I wouldn't be too concerned that the story would start to focus on developing a cure with that information. If anyone were capable of using that information to create a cure, there's a very small chance they'd have the opportunity to do so because it would require very specific circumstances to make it a reality. First off, it would obviously require someone with that set of skills still alive and able to survive this long. Then of course, they would have to aquire the knowledge that humans born after the infection are immune to turning. They would have to see this firsthand to know that it's true and finding someone born after the infection is gonna be hard when a large amount of the population in the world has been killed. Even if they find someone born after it and witnessed them die without turning, they can't do much more with that information if they don't have other test subjects to learn more from studying and since death would be the only way to confirm immunity, they'd be waiting for newborns to be discovered or created, just to wait for them to die to study.

So in the end, introducing the idea of newborns being immune would never work as a story of finding a cure. However, newborn immunity could create a more specifically targeted end game which they already have in The Walking Dead, surviving for a better future. Introducing it in the show won't change the fact they're still surviving for each other, for their family to have a sense of security and a future. The only difference would be that they have an assurance that if all previously inhabitants of earth die while a new generation lives, they'll have better opportunities of recreating a world free of the dangers of walkers.

TL;DR: Newborns being immune isn't a game changer, it's just a goal they'd be more capable of making a reality.