"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Mophie's Upcoming Juice Pack Air is First Qi-Certified iPhone X Charging Case
While there are already iPhone X battery cases on the market, Mophie's accessory is the first to be Qi-certified by the WPC. This certification program encourages manufacturers to submit verification that their products comply with the latest Qi specifications, and subsequently allows customers more peace of mind when purchasing products, knowing that they will support devices like the iPhone X, 8, and 8 Plus.
The Juice Pack Air for iPhone X is described as a "form fitting case for the iPhone X," with a 1,720 mAh battery that provides "an additional 9 hours of talk time." Comparatively, the Juice Pack Air for iPhone 7 has a 2,525 mAh battery and the iPhone 7 Plus accessory has a 2,420 mAh battery. In the sole image posted to the Wireless Power Consortium's product details page (seen to the left in the above image), the accessory appears in black. Mophie sells similar Juice Pack Air products for other iPhones in up to five colors, like Navy and Rose Gold, so other colors could be coming as well.
Like those products, Mophie's Juice Pack Air for iPhone X would let users charge up the battery inside the case, and when their iPhone X begins to die, they could flip a switch and begin fueling up the iPhone while on the go. The Juice Pack line is compatible with Mophie's "Charge Force" ecosystem, so it can be placed on accessories like the Charge Force Desk Mount or any other Qi-enabled mat.
Mophie currently sells Juice Pack accessories for the iPhone 7/7 Plus, 6s/6s Plus, 6/6 Plus, SE, 5s, and 5, as well as a few other Android devices, typically priced at around $100. The only wireless charging accessories it has listed on the iPhone X's page are the Wireless Charging Base (also sold on Apple.com), the Charge Force Wireless Charging Base, and Charge Force Powerstation.