This may be hard to believe, but when i was exploring a stronghold in the xbox 360 edition, i found an End portal frame laid horizontaly one square above a pool of lava. I didn't really know how to use it (using an ender eye or something like that) so i left it alone. Even though it may be impossible to utilize my discovery due to the fact that the End does not exist and doing so might freeze my game, i'm still curious as to how it got there.
They put it in probably for a place holder so people would not have to start up a new world for the end when it comes out in the next update...
Although regardless I would probably start a new world just to have jungles when they come out...:D