It's been said time and time again throughout these boards but Wanda and Pietro would make much more sense in the Avengers, NOT the X-Men films. While they are mutants, that is not where the majority of their history lies. Looking at their comparative history in the comics, they were with the Brotherhood for less than a year. They started in Uncanny #4 and left in Uncanny #11. That's 8 issues. 8 issues! Does that really sound like such a rich history that they absolutely have to belong in the X-movies? No. If you have to look at spin off material like the cartoons and alternate reality comics in order to find any decent inspiration for including them in X-films, then you're stretching for it, so stick with people in the main comics who would make much more sense and have much more history than them.
And as for those who say, "Let them show up in future Magneto or First Class films", lets just get the first out of the way to begin with. Both of those films, especially Magneto, have a TON of things working against them at this point. Magneto is a film being made about a character that most fans don't really think could use a separate film, the film in general doesn't really appear to be a high priority for barely anyone involved considering the rather quiet and small amount of news we're getting on its production and how damn near everyone involved in it have other project they're gonna finish before Magneto, and the bit of backlash from other recent films, this film would likely have to be a monumental success to even think of getting a sequel. Same goes with First Class, considering that it needs to even rely on the success of other films before it will even be considered for a green light.
Marvel is being smart and keeping the rights to them to their studios, instead of tying them down at Fox to a franchise that is somewhat struggling, so that they can use them where they would be much more lucrative.
