Except it's fast forward years ahead of the last time we saw her and it's a variation of the power we've seen. Would you have rather been told she has a new power before you saw her use it? IMO, the dimenstration in THE FIRST TEN MINUTES OF THE STORY is better then waiting for a diologue 30 or so minutes in. They hit the ground running. You weren't supposed to expect it.
Take the first extraction in inception for example, we all knew they would enter a dream world, but the layering effect hadn't been mentioned in the trailers. So when they woke up in one dream, only to find they were in a dream within a dream, you could say that's cheating or you could say that's how the writers wanted to show the audience dreams could be layered so as to set up the climax. Like in DoFP, the writers opted to show, rather then tell in the scene that INTRODUCED the characters and their powers in THIS film. The sentinels weren't established as existing in any other movies, and were only teased in x3. Yet here they are shown to adapt without any explanation in the middle of the fight sequence. At this point the mystique DNA hasn't been reveled, so you can call that a Deus Ex Machina too. Or you could call it a dramatic reveal. Sometimes you can have those without them automatically being DEMs.
Furthermore, the established rules for powers in previous movies have been that there are no rules. There have been characters that dramatically evolved in power sets in the past for the sake of plot. Nobody was crying DEM when it was revealed Jean grey had another more powerful side to her the entire time (that we had never seen) when she became the Phoenix. If you didn't know it happened in the comics first you would never have expected her to be back in the 3rd. Especially so much more powerful and evil (even with the teases in x2s ending.) so it was an unexpected solution to the problem of Jean greys death in the first act of x3, but would you really call that a DEM? Moreover, the existence of Phoenix in past story lines sets up the possibility of mutants being able to evolve beyond there current power set. And that's what kitty did. Her power mutated. In the 10+ year gap of stuff happening we don't see. So not only can we expect that some things are different, but with it the rules of this universe, it shouldn't surprise us that a character has a new power spun off from her old one. And we shouldn't get mad when they show us this new power to introduce us, rather than tell us about it, and have to take the whole plot of the movie on the word of one character.
This is a time travel story. I think they introduced time travel in the most natural way they could have. How would you have introduced time travel in a less contrived way?
