I think 4 actors of each timeline would be perfect, and more than enough to have great photos of the impressive cast for the press and fans alike.
On other hand, after seeing the latest Game of Thrones individual posters, I think one shoots like those would be really great for this sequel.
So I couldnt resist to do this:
Imagine posters like these with all the main characters, including Mystique, Rogue, Kitty, Iceman, Beast, Magneto and co.
Fox HAS to do it, the more posters, the better
Next Big X-Men Crossover
* 2017- X-Men: Age of Apocalypse
Edit: Forget about 2017:
Official announcement -> X-MEN: APOCALYPSE - MAY 27, 2016!!!!