Apple has several dual-camera smartphone models now, but other manufacturers including Huawei and LG already have devices with at least three. Samsung even released a mid-range model, the Galaxy A7, with a triple rear camera setup. Adding a third camera would let Apple offer more consumer-friendly photography features like telephoto closeups and improved "bokeh" blurred backgrounds. A three-camera iPhone has been rumored before, as shown in the render below.
According to the WSJ, Apple isn't necessarily keen to build another budget-oriented XR device. However, the next model has been in development for months already and it would be too difficult and costly to switch gears. By 2020, it plans to build all of its iPhones with OLED displays, which offer superior contrast and color reproduction.
iPhones are looking less competitive every year against models from Huawei and other companies that are now at least as technologically advanced. In that sense, it'll be interesting to see how it proceeds over the next year to try to regain its advantage. In the meanwhile, though, it still has to sell iPhones, so it seems that XR devices will remain until at least 2020.