If you would actually read, I was talking about three years from now, plus the two it's already been supported, which is five. And no, I am going by Apple's history, no my own assumptions.
You didn't explicitly state 3 years from
now. You implied it, and I misinterpreted that - that's my bad, apologies there. Still, it doesn't change that Apple could support the 6s for longer than what you consider historical....
The point I was getting at with regards to the 4S and 5 is that both of those devices had been supported for an extra cycle than prior devices. Why? Well I'm sure it was a lot of factors, from how long those devices were in the market for, but processing power plays a role and probably the biggest role.
The poster you responded to identified the 6s as having enough power, which is a key point to make about the device... it is significantly more powerful than the 4S which has to date received the most iOS upgrades yet before officially being unsupported. We may see the 5 tie it come WWDC but that could be more due to the 64 bit app focus Apple has, as the 5/5c runs iOS 10 much better than the 4S runs iOS 9. But this can also be attributed to processing power.
That is why I also mentioned the Macs. Those old macs/macbooks that are getting Sierra are much more powerful than the 4S....but not so compared to the 6s. What changed? Did Apple stop supporting them based on apparent history? No, they support them as long as they felt those computers were capable of running the latest operating system. Apple has a history of doing this as well.
If one wants to use history as the main point for how many updates the 6s might get, we should also look to Apple continuing legacy support the more powerful the device gets, not limiting it...both for phones/ipads and for their computers. Consider the extent mobile chips have come these last several years.
Neither one of us can peer into the future so we can't say for sure. For all we know, you could be right on the money. iOS 13 could be so taxing on the current devices that it will demand 6GB of ram or something. But at the same time, to imply only 3 more years is
most likely, is to ignore how the 6s is different from previous iPhone generations