This isn't new at all. Apple has been consistent with long term updates for a while.
iPhones have been getting at least 5 major annual updates sense the iPhone 4. The average is 6 updates.
If anything, it gets to a point where the old hardware can barley handle the newer OS.
This is the equivalent of them promising to be called Apple in 5 years - it changes absolutly nothing.
https://en.m.wikipedia.org/wiki/IOS_version_history
Edit: thinking about it, this gives them an excuse to reduce the number of years they support phones. Instead of 6-7, can we now expect that to become only 5 years?