Personally, the only thing that'd really concern me is over time, is it possible the iPhone can warp from normal use in a normal non-skinny jean pocket. (I already know from experience with Galaxy Notes, the answer for them is, no, not even a remote chance. For the iP6+, I'm not sure, but I'm guessing it too won't really have any problem with most people's use.)
But deliberate bend tests are kind of stupid to me.
It's along the lines to me of "Gee, could I screw up my MacBook by purposefully bending the screen? Can this 2 cent nail screw up my HDTV if I drag it across the screen? Can this brick mess up my car?"
The answers are pretty obvious. Only real world use will answer the real questions- if in a couple months to a year from now lots of normal users of iP6+'s have bent phones, then I'd see a huge problem, not just because you can deliberately break it (like most *ANYTHING* really).