"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Intel Announces Thunderbolt 3 With USB-C, Single-Cable Support for Dual 4K Displays at 60Hz
"Thunderbolt 3 is backed by Intel's new Alpine Ridge controller. USB 3.1 support is provided by integrating a USB 3.1 host controller into Alpine Ridge. There will be two flavours of the controller, one that uses four PCIe 3.0 lanes to drive two Thunderbolt ports, and another version that only uses two PCIe lanes connected to a single Thunderbolt port."
Thunderbolt 3 is capable of driving up to two 4K external displays at 60Hz or a single 5K display at 60Hz running off a single cable. Dell and other manufacturers currently use a dual-cable solution for most 4K and 5K external displays, since the current DisplayPort/Thunderbolt spec does not provide enough bandwidth to drive the high-resolution monitors. Thunderbolt 3 also supports more protocols than any other I/O controller, making it compatible with virtually any dock, device or display.
Intel expects initial products with Thunderbolt 3 to start shipping before the end of this year, and ramp up in 2016. Thunderbolt 3 is rumored to launch alongside Intel's next-generation Skylake chips, succeeding the Broadwell line, later this year, and the new spec could theoretically be included in Skylake-based Macs that could possibly be released in late 2015. Refreshed Macs would likely gain USB-C ports integrated with Thunderbolt 3 as an all-in-one solution.