The Past, A New and Uncertain World, A World of Endless Possibilities and Infinite Outcomes - (NEW mid-late 1980s)
We had a wonderful movie to wrap things up. Let's talk about what's next.
We know that "Apocalypse" will be a sequel focusing mainly on the First Class cast. That leaves us with Xavier, Magneto, Mystique, Beast, and potentially Havok. Young Cyclops, Young Jean, and Young Storm have been seemingly confirmed too. Channing Tatum as Gambit is already confirmed also. It has been stated that Quicksilver will play a bigger role in the next film. Bryan Singer has said that he wants to use Nightcrawler in Apocalypse. That's already a fairly packed cast of 9 or 10, especially when it's all but guaranteed that Wolverine will be part of the main cast.
It's hard to say when Apocalypse will take place, but I think a fair guess is mid-80s at the very least. We know Jean was somewhere inbetween 10-12 in 1981 because of the third movie, so aging her 4 years at the very least allows them to be teenagers (and running a nice symmetry with the All New X-Men comic book). We also already saw Scott as a teenager in X-Men Origins: Wolverine (1987) so it would be nice to see him around that same age again with more discipline and leadership.
The only problem is aging the First Class cast so much again. McAvoy and Fassbender just played characters that were 4-6 years older than them in DOFP. Aging them another decade is going to take some work, but I definitely believe that it can be done.