According to MTV on Feb. 19, J.J. Abrams stated that Klingons will be appearing in the new "Star Trek Into Darkness" film. Even though that John Harrison is a key focus villain opposing James Kirk, there's no denying other adversarial villains such as Klingons being in the sequel. So rest assured, they will be back.
Abrams stated that there was a scene that was cut from the original 2009 "Star Trek" film that involved Klingons interrogating Nero and trying to retrieve knowledge he already has extracted from The Federation of the future. But that wound up on the cutting room floor and on the "deleted scenes" section of the Blue Ray/DVD.
Also, Abrams recognized the role of Carol Marcus, played by Alice Eve, as a rumored love interest to James Kirk in "Star Trek Into Darkness". Abram's states, vehemently, "Wouldn't he like that?", but surmised there wouldn't be any typical romance involved. Abrams will have his own version of their coupling up in such an action/adventure film. In "Star Trek II: The Wrath of Khan", back then she was the mother to Kirk's son David who was killed by a Klingon while being interrogated in regards to secrets regarding "Project Genesis".
Thus, solidifying the adversarial role they will be playing in "Star Trek Into Darkness". The characters relationships all tie together from the old to the new.
With all the focus on the main villain, John Harrison, it's time to switch focus to the Klingons. Considering that there is a degree of certain Trekkie common knowledge of Klingons already. Abrams states, "You don't need to know any preexisting stories to enjoy this film".
That being said, the existence of Worf in both "Star Trek The Next Generation" and "Star Trek DS9 has already shown historical significance to the science fiction genre which has been ensconced into TV's pop culture.