As pointed out on Neogaf, Telltale Games talked about The Walking Dead: Season 3 during a panel at the PlayStation Experience event. The developer assured that in 2015 we will ge getting more specific news about what will the next game in the series focus on, but we may have to wait a while to play it.
Questioned about a 2015 release date, Telltale representatives opted not to commit. Considering the developer now has their hands full with Tales from the Borderlands and Game of Thrones, it's very likely we'll have to wait till the end of 2015 or 2016 for Season 3 of The Walking Dead.