You may recall during Microsoft's E3 presentation of Halo 4, Master Chief was fighting a group of Covenant enemies, despite the race's newfound peacefulness.
As it turns out, this group was part of the Storm Covenant faction. Revealed in the latest issue of OXM, the Storm is a group of Covenant that have broken up with the main body and now follow their Prophets' ideology and religion with them. Their goal, according to the article, is to find a powerful weapon on Requiem, though details remain vague.
Nothing is really known about the weapon either except that the Prometheans are intent on guarding it and will do anything they can to protect the Covenant or UNSC from acquiring it.
Other than that, the article seems to touch on previously known details about Halo 4 like the co-op campaign, competitive modes, and some of the Promethean enemies Master Chief will encounter.