16GB will become totally useless for iPhone 6s series. To fill it up. simply take multiple pictures or a short 4K video.
I hope, Apple could increase entry level capacity to 32GB, although I will always go to the maximum I can get when I change/buy a phone.
I'm an entry level iCloud subscriber ($.99 a month plan) and have no issues with photos/videos. When I plug my phone in at night they simply upload to the cloud and off my phone...i take LOTS of pics and videos too. If I want to view them, boom they stream to my phone from the cloud and they're there without sacrificing HD space.
I'd gladly spend $12 a year for iCloud vs getting a >16 gb phone and pay that premium. The apps I use I use. The ones I don't I delete and redownload if and when needed.