From Blastr here, it's gonna happen. The Walking Dead spin-off has been green lit by AMC. This is nuts but in an insanely great way! With TWD entering season 4, you get the feeling that while the series is still fresh, we are probably towards the midpoint of the gang from Atlanta.
But to have another series take place in tandem is fantastic. Reminds me of Star Trek The Next Generation with DS-9 and Voyager all going on. Or Stargate SG-1 seasons and Atlantis overlapping.
And not only that. The TWD series has open-ended possibilities. What's going on in other parts of the world? How did it happen? Is there still a major human population with thousands, tens of thousands, or even hundreds of thousands in a city safe from the walkers, all waiting to be infected?
The possibilities for such a series or even more materials are endless.