With the features such as the QuickType covering more of the screen I can't imagine myself going back to a smaller screen. I tried using my iPod touch with the feature and it just ruins the experience.
If you have the money than doing the 6S+ and SE swap is the best of both worlds. There are times that the SE just makes life a lot easier and other times that having the real estate of the 6S+ is great. Not looking to argue with Sangs... but when I go to Red Sox games.. The SE is the perfect phone for the day.
I have an international trip coming up in September and I need to decide on what tech I am bringing. Do I bring a Duel SIM phone and just plop a local SIM in or take my two Iphones and just pay the rates? Such First World Problems... LOL