“Through the editing process, the sequence became extraneous,” Singer said. “It’s a really good sequence and it will probably end up on the DVD so people can see it. But like many things in the editing process, it was an embarrassment of riches and it was just one of the things that had to go. Unfortunately, it was the one and only sequence Anna Paquin was in, the Rogue character was in. Even though she’s in the materials and part of the process of making the film, she won’t appear in it.”
Singer explained his reasoning for this in further detail.
“She did a fantastic job. She was awesome in the sequence. She’s a brilliant actress. I would work with her in a heartbeat.
”She completely understood,” Singer continued to explain to EW. “It’s very disappointing, but she’s very professional and she knows that stuff happens, particularly with material you shoot early on in production. Films evolve.”
Almost immediately after this news broke, fans went into knee-jerk reaction mode. This should be no surprise because the comic book fan base is known to overreact to news they are not be happy with. (See Heath Ledger being cast as the Joker, Ben Affleck cast as Batman, the reaction of a then-non-action star in Robert Downey, Jr. being cast as Iron Man, etc., etc.)
But let me get to my point and that's to say X-Men Days of Future Past is meant to not only fix the two X-Men cast time lines that are established in the X-Men movie universe, but it is being done to reboot characters from the older, future timeline as well. This means, eventually, Rogue, Cyclops, Jean Grey and several others will be rebooted into the younger X-Men cast with new actors. In Days of Future Past, history is being rewritten by Wolverine and the X-Men: First Class cast so there can be a new future for the X-Men. This means the older/future timeline will completely change or be canceled out entirely.
Again, this knee-jerk reaction to Rogue being cut out is no surprise but what is a surprise is that it's a single scene which had the female mutant in it that is being cut. Obviously, this scene was irrelevant to the plot of X-Men Days of Future Past. Even Singer himself said, "the sequence became extraneous." By the way, extraneous means "irrelevant or unrelated to the subject being dealt with."
So Rogue was put into X-Men Days of Future Past in order for her to just make an appearance. But then, as Singer also mentioned, films evolve and change during the film making process. Script even get rewritten during the filming process, as well.
There's a very high probability that Rogue will be back as a new female actor since her power set is one of the more interesting of any X-Men team member and makes for great viewing on the big screen. Just be patient and you'll see.