"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple’s 5K Thunderbolt Display Could Include Its Own Graphics Card
Stephen Foskett and Daring Fireball's John Gruber speculate that Apple could potentially introduce a refreshed Thunderbolt Display with a built-in graphics card, which would result in a display able to work with almost any Mac because it would be driven by an internal graphics card rather than the machine it's connected to.
9to5Mac is floating a similar theory, claiming it's heard rumors Apple is indeed working on a 5120 x 2880 display that has an integrated GPU. Such a display would likely require the purchase of a newer machine with USB-C or Thunderbolt 3, but it would work with Apple's notebook lineup going forward.
A noted analyst doesn't believe Apple will go to the trouble of introducing a display with a built-in GPU, instead releasing a 5K display that will connect with newer Macs over Thunderbolt 3 by taking advantage of both DisplayPort 1.2 streams.
It's been believed Apple would wait to introduce a 5K display until DisplayPort 1.3 support is built into Intel processors as the standard will allow for plug-and-play support for 5K external displays, but by using both of the DisplayPort 1.2 streams, forthcoming machines that include Thunderbolt 3 ports will be able to drive a 5K display using Multi-Stream Transport without the need for an external GPU.
Multi-Stream Transport (MST) would stitch two halves of a display together to make a single seamless display, with each DisplayPort 1.2 connection driving half of the display, a technique Apple previously used in the first 5K iMac. The 5K iMac used the internal equivalent of a dual cable DisplayPort 1.2 MST setup.
Multi-Stream Transport is inferior to the Single-Stream Transport that would be possible with DisplayPort 1.3, but DisplayPort 1.3 support is not built into Skylake or its successor Kaby Lake, meaning it will be at least 18-24 months (the time until Intel's Cannonlake processors launch) before Apple can introduce machines powerful enough to drive a 5K display over a single-stream cable.
With the Thunderbolt Display having gone without an update since July of 2011, another two years is a long time to wait for a refreshed display.
There is no concrete word on when Apple will introduce a new Thunderbolt Display, but given the stock shortages and the rumblings that a successor is in the works, there is a possibility an announcement could be made at the Worldwide Developers Conference.