VESA, the standards body responsible for such luminary technologies as DisplayPort and the omnipresent VESA monitor mount, has published the specification for version 1.4a of Embedded DisplayPort (eDP). The new standard builds upon DisplayPort 1.3, which was published at the end of 2014. In short, eDP 1.4a allows for laptops, smartphones, tablets, and all-in-ones with 8K displays (7680×4320) or high-frequency (120Hz) 4K displays—but it includes a few other neat features, too.
eDP 1.4a appears to be almost entirely based on DisplayPort 1.3—which was published in September 2014—with a couple of new features thrown in for good measure. eDP 1.4a specifies four high-speed (HBR3) lanes between the graphics adapter and display, with each lane capable of 8.1Gbps; the lanes can either be used individually, in pairs (more on that later), or all together for a total theoretical bandwidth of 32.4Gbps. That's enough bandwidth to drive a 4K display (3840×2160) at 120Hz with 10-bit color or an 8K display at 60Hz.
So sometime in in late 2015 or early to mid-2016 for iMacs and Mac Pros to be able to use this to support beefier external displays?