I think Judith is their backup in case Chandler leaves the show, Carl's popularity drops, or they have some scenes he is just to old for. I say his popularity drops because I am convinced that is why Lori and Andrea were killed off so soon. Since then, the other characters, like Carl have had significant changes to make them more likeable (i. e. Carol, Michonne, and Beth, okay, not so much Beth, which is why I expect Beth to die at the end of this story arc.) Also, I think they are keeping Judith to replace Carl in those scenes from the comic that are still great scenes, but need a younger character for maximum impact. Or even for new scenarios that the writers think up that Judith is better suited for than Carl because of his age now.
I don't think so and I only say this because Judith is too young to replace Carl. They would have to have a 10 year span go by between seasons.
Carl is supposed to be a teenager, right? I know that my own niece went from last June's awkward, kinda plump, 5'2" Jo to a gorgeous taller than me and I'm 5'6" pin up worthy young lady in June of this year That was 14 to 15. It's disturbing but normal. Carl's turning from a child into an almost adult is not at all jarring to me and doesn't affect my enjoyment of the show. At that age, that happens. It is weird to see S-1 and S-2 Carl and now S-4 and S-5 but between last and this season, I'm not at all surprised at his growth.
As for Judith taking Carl's place, that seems far fetched. She is a baby. How long will the show last? I hope for a long run but can't see it lasting forever. I'm glad (or hope) that disrespectful Carl is GONE. That shit pissed me off.
If they keep having time jumps to accommodate Chandler's growth (and I think they will for the next two hiatuses, at least), then it will not be long before Judith is old enough to take Carl's place. Carl is only 7 when the comic starts. If they have a time jump during the next hiatus, Judith will begin S6 ~2-3 years old, and after the next hiatus, she could easily begin S7 ~4-5 years old. At 5 years old, I think Judith could begin to fill in for Carl. Not to mention that by that time Carl (nor Chandler) will be a kid anymore. He will a young man of about 17/18. At that point, even if Carl stays, they will still need someone to play "Rick's kid" on the show. Who better than Judith?
As for for the future of the series, TWD is not going anywhere any time soon after breaking another ratings record with over 17/21 million viewers depending on how you are measuring. TPTB renewed the show for S6 before the season started and that record breaking premiere all but assures of a S7. When shows are being renewed with a third of that viewership, I see TWD easily being around a few more years. The producers have already shared that they have enough material and have basically already plotted out through S12.
I say all that to say that in just a couple of years, I can see Judith being used to cover material Carl couldn't because Chandler aged to quickly for them to cover it.
I do think that there is some truth behind the show killing off unpopular characters. However, Carl has generated a lot of heat (I hesitate to use hate, but it's probably true) and has never been very popular. Especially back in Season 2. I remember him topping some "Most annoying characters" lists.
It feels to me that they are trying to work on his character to make him less annoying and part of it is a natural character progression.
I agree that they are trying to work on Carl's character, but if they are unable to succeed (fans are a fickle bunch), I can see Carl being killed off, especially if Judith becomes a very popular character. I can see that happening too, especially if they cast a gifted young actress like Maisie Williams or a young Dakota Flanning.
Once Judith is 3-4, I think it will be very interesting to watch her grow up and see how she processes the world, especially since she won't have any memory of the pre-ZA world and the type of humanity her babysitter Tyreese is trying to hold onto. Will she be like Sophia/Mika, Lizzie, Carl, or someone altogether different, especially with Rick now embracing his brutality and trying to balance that with his humanity? Maybe Judith will be able to succeed on that front. Maybe not. My vote is for someone altogether different. That in my opinion would be the most interesting to watch.