Apple won't be first major vendor out of the gate with a 5G smartphone, but it may have a comprehensive lineup when it's ready. Historically accurate analyst Ming-Chi Kuo now expects all three 2020 iPhones to support 5G, not just the two highest-end models. Apple will be helped by falling 5G hardware costs (you could see limited 5G support on $250 Android phones, Kuo said), more resources thanks to the Intel modem business acquisition and expectations from both carriers and customers. At that stage, 5G may be treated as a given in the iPhone's price class -- and carriers might not offer as many subsidies without 5G support.
The trio is expected to handle he millimeter wave 5G you find in the US as well as the sub-6GHz access found elsewhere. This doesn't guarantee that you'll always have cutting-edge wireless, but it could represent better coverage than the early days of (very patchy) LTE.
Rumors have continued to swirl about other, more tangible changes, including different screen sizes across the line (ranging from 5.4 inches to 6.7 inches) to a smaller TrueDepth camera, a smaller notch and laser-assisted rear cameras. Add 5G to the mix and this could be a more substantial revision of the iPhone than what many expect later in 2019.