The Walking Dead showrunner Scott Gimple had previously teased that new characters will be introduced in the upcoming Season 5 of the show. He also confirmed that deadly villain - Negan will definitely be making an appearance in upcoming episodes.
If anything, it's a clear indication that he may turn up at the end of this season (typical of final episode material to lead into the next season). Either way, Negan in the TV show (be it this season or next) will be impressive nonetheless. Kinda wonder if what happens with Glenn will occur in the show or not.