I can see it happening if they're going to release another 5.8 inch OLED model. Continuing to sell the 10 would be pointless at that point, especially if the newer model is going to be cheaper than the current or the same price as the reduced price of the 10.
iPhones are routinely discontinued. Some sooner than others. This really isn't news. It is just the way one person titled their article to get web views and a lot of the internet copied the link to the story.
Nothing to worry about. Apple always offers hardware and software support several years after.