Re: The #4 movie - which movie series will have it first?
They asked him in an interview "is it possible to come out of this movie with the First Class series, the original X-Men series and an alternate timeline series that was featured in the movie?"
Singer replied "Yeah, it's very possible. And that's not counting all the other characters not yet explored because the X universe is so vast."
That right there tells you that while this is a continuation of both, both FC and the original trilogy can be continued in their own right still. Meaning we can still get an actual X-Men 4 after this movie.
1) Man of Steel 2) Thor 2 3) The Wolverine 4) Pacific Rim 5) Iron Man 3 6) Oblivion 7) Mortal Instruments: City of Bones 8) Ender's Game 9) Beautiful Creatures 10) After Earth