Any concerns 20th Century Fox may have had about moving forward on X-men: Apocalypse have been wiped away by X-men: Days of Future Past's huge opening weekend. What we've heard previously is that it will be a direct sequel and will focus on the younger characters, but that may not be entirely the case and we may again see time travel factoring into the story.
Kinberg: "It will focus primarily on the 'First Class' cast, but it will certainly have some of the original cast involved, too."
Patrick Stewart hinted some time ago that there were plans for Charles Xavier post 'Days of Future Past', and this may be what he's talking about. Apocalypse is an immortal mutant who has lived for thousands of years, and continues to be a thorn in the X-men's side far into the future, so it wouldn't be surprising if he's menacing both teams. It seems a little bit early for Bryan Singer, who Kinberg says is still expected to direct, to try and adapt the classic Age of Apocalypse storyline. The groundwork for something of that scope could be set in this next film, though.
X-men: Apocalypse is due to open on May 27th 2016.