Why would Kishimoto end it on chapter 700?
"Because it is a nice round number?"
That's like saying I am going to end my Fanfiction on Chapter 10.
It will end when it ends.
Further - I'm not convinced of the theory that it is going to end "this year."
While things are getting pretty close to what could be a logical end - there are still plenty of things to keep the story aloft through 2015.
I imagine he also has plans to continue the Naruto universe (or has a plan for a continuation if he were to do one) that would be akin to the time skip between Naruto and Shipuuden. It would not be the first time in manga history for authors to take a break from a popular series to return a few years later to pick up with a continuation of the plot.
So we're really just looking at the completion of this story arc, in either case - and that could be wrapped up "this year" while the subsequent series (still within the Naruto universe) could carry on to round out the entire universe.
But I don't really buy all of the claims of when the story is or is not going to be completed by. It's like asking an artist when he's going to finish his painting, and author when he is going to finish his book (or book series), a mod team when they will consider the mod a completed and closed project, etc.
Even if Kishimoto has a plan for when that might be - it's highly likely that reality will deviate from the plan.
