"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Intel Launches New Skylake Chips Appropriate for 15-Inch Retina MacBook Pro
The direct upgrade path for the 15-inch Retina MacBook Pro would use the following quad-core chip options: a 2.6 GHz Core i7-6770HQ, a 2.7 GHz Core i7-6870HQ, and a 2.8 GHz Core i7-6970HQ, all coming in at the same price points as the Haswell variants currently used in the MacBook Pro.
Perhaps a more intriguing but less likely scenario involves a series of new mobile Xeon E3 chips. These chips could offer even better CPU, graphics, and memory performance, although pricing becomes an issue with the highest-performing chip in the family.
As for the 13-inch Retina MacBook Pro, Intel announced chips appropriate for those machines back in September, although it suggested the chips would not actually be launching until early 2016. Those chips have been included on Intel's price lists for several months, but have been slow to show up in the wild. A claimed benchmark for a 13-inch MacBook Pro running one of these chips last week appears to have been a fake.
Most of Apple's Mac lineup is in need of updates, as Intel's Skylake delays have hampered Apple's ability to launch refreshed models. But with the Skylake logjam finally starting to break, Apple appears set to update its entire notebook lineup over the next several months. Opportunities for major product introductions could come at Apple's rumored March media event or at WWDC likely scheduled for mid-June, although smaller updates could come at any time via press release.