Apple's iPhone 9 and Xs to only come with Intel modems, dual SIM support in the cards
First off, Apple is apparently done with Qualcomm for good, and all three upcoming new iPhones this year will be equipped with Intel modems. Thus, unless Qualcomm wiggles back in the supply chain due to some patent suit agreement, there won't be the differences in download speeds and signal strength that we are witnessing now between iPhones with Intel and Qualcomm modems.
Unfortunately, Intel may not be ready with a robust 5G modem offering by the time the iPhone 9, Xs and Xs Plus hit the shelves, but US carriers will have phones hooked up to their 5G speeds in early 2019 at best, so it's not that big of a miss.
The more important extra features that are coming to the iPhones' cellular modems this year seem to be Gigabit LTE connectivity, and dual SIM dual standby, though whether or not Apple will implement that particular option is anyone's guess. Still, Intel's new modems will be offering it, so perhaps the more affordable iPhone 9 could sport a dual SIM version, at least in places where such models are popular, like in Asia.