Future proofing as in the 3D touch. More and more 3D touch support being added as time goes by. Both from Apple and third party developers.
Having said all this... I'm using a SE in anticipation on what the 7 brings. If the battery doesn't improve or at least slightly shrink in size then I'll use the SE until 2017 when the supposed 8 comes out. It too late in the cycle for me to justify paying for the 6S.