The trailer looks awesome but Zuko and Mai actually kiss. And it's not a peck like with Jin, it's a Sokka/Suki-Serpent's Pass kiss. All the Maiko's are going crazy over it, but I'm not worried. Zuko's an idiot and he'll get over it. They show him leaving the fire nation anyway, so I believe he'll join the gaang eventually. Poor Iroh though, he's only in one clip.
Okay, I'll post my theory regarding the Maiko kiss now. I believe that Azula wants to keep Zuko in the Fire Nation because the last thing she wants is for him to leave and join up with Aang. Therefore she decides to give him everything he wants and needs to be happy (at least what she thinks is everything.) He's accepted back into his home and his family, and has regained his status. Using Mai's affections for Zuko, Azula also plans on having Mai seduce Zuko so he's has someone to be with, to make him happy.
He has everyone thing he could ever want, except Iroh's favor. Eventually he'll realize that he needs to leave for one reason or another and therefore, have to break-up with Mai. I believe that episode 7 "the runaway" is what this signifies.