It would be pretty stupid from Apple to bury their heads in the sand and pretend this is not an issue... hence I believe the new 6+ are with fixed panels.
Without a doubt there will be a difference in design (internally) for the 6s, but will apple communicate that to us? I doubt it, as they'd be all but admitting the iPhone 6 plus needed such a fix, i.e., its weak and can bend.
Think of the brouhaha that would erupt over that admission.