"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Adds High-End 15" Retina MacBook Pro to List of Macs Supporting Dell's 5K Display
Dual-Cable DisplaysDell's dual-cable 5K display requires more bandwidth than is currently supported over a current single DisplayPort cable, so it uses a dual-cable solution that takes up two Thunderbolt ports on a Mac. The availability of Intel's Skylake platform with DisplayPort 1.3 support later this year will enable Apple to update Macs with support for external 5K displays that function over a single cable, at which point the company could theoretically release a 5K Thunderbolt Display.
Some displays with resolutions higher than 4K require two DisplayPort cables to connect the display at full resolution. With OS X Yosemite v10.10.3 or later, the Dell UP2715K 27-inch 5K display is supported on the following Mac computers:
Mac Pro (Late 2013)
iMac (Retina 5K, 27-inch, Late 2014 and later)
MacBook Pro (Retina, 15-inch, Mid 2015) with AMD Radeon R9 M370X
The support document also lists the high-end 15-inch Retina MacBook Pro as capable of driving most single-stream 4K displays (4,096-by-2,160) at 60Hz on OS X 10.10.3, becoming the first notebook to support single-stream 4K displays alongside the Mac Pro (Late 2013) and iMac (Retina 5K, 27-inch, Late 2014 and later).
Apple initially listed the high-end 15-inch Retina MacBook Pro with AMD Radeon graphics as capable of supporting an ultra-wide display with up to 5,120-by-2,160 resolution at 60Hz, but has since updated the notebook's technical specifications to reflect its ability to drive a single external display at up to 5,120-by-2,880 resolution at 60Hz.