Was Breaking Bad PG-13 though? It didn't feel like it, Breaking Bad may not have been as hard core as say Game of Thrones, but it was at least a soft R, rather then a PG-13. A lot of the violence and language seemed R rated in that show, maybe not the sex, but I wouldn't say the show was PG-13.
I do have some faith in AMC in this matter, I just would hope Seth Rogen wouldn't mettle to much with the source material. He ruined Green Hornet for me in that movie, so I am hoping he doesn't change things too much to fit his style of story telling.
Though I do wonder if some aspects of the source material would be too controversial for AMC, some of the characters seem like they could cause a real stir. I also wonder if it wouldn't be for the best, if they made it a period piece and set the whole show during the 90s. The Grail's plan seemed to based around the beginning of the new millennium.