Not really Darth. Before X3 even came out, the studio and producers were planning spin-offs and prequels. That's because the movies were becoming expensive and also difficult to get all the cast together. I'm sure the production problems of X3 didn't help - not being able to get a deal with Singer, Singer then leaving, Vaughn then leaving, etc. The franchise was becoming trickier to manage, so they wanted to go smaller and less expensive.
Of course, this was all before Marvel Studios began releasing movies. Fox and Sony were the comic book movie kings at this time. And, sadly, studio bosses didn't really see the huge long-term value of the 50 years of X-Men comics that Fox had rights to. They just wanted to wrap X-Men up in three films with a nice, neat trilogy then explore some spin-offs. It turned out to be a very unwise way of thinking.
It's pretty staggering that a studio would have film rights to 50 years of comics (X-Men and F4 both appeared in the early 60s) and not exploit that to full potential by mapping out a franchise far into the future. How many other times does a studio have half a century of classic stories in its grasp?! Studios are always looking for franchises - and trying to make films into franchises - and yet in this case they didn't see what they had right in front of them. I guess 50 years of comics are not as easy to comprehend as one series of books (like Potter, Twilight, Hunger Games, LoTR).
However, they are now waking up to the idea. Thank God.