At Computex 2015, Intel has unveiled Thunderbolt 3. The headline feature: Thunderbolt 3 has changed its connector from Mini DisplayPort to USB Type-C.
In addition to the new connector, Thunderbolt 3 now also supports USB 3.1 (i.e. Gen 2, up to 10Gbps), and the Thunderbolt transport layer sees its max bandwidth doubled from 20Gbps to 40Gbps (bi-directional, full duplex). Thunderbolt 3 also offers an optional 100W of power, in accordance with the USB Power Delivery spec. Without USB PD, Thunderbolt 3 will provide up to 15 watts.
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.
With the increase in max bandwidth, Thunderbolt 3 now supports up to two 4K @ 60Hz displays or a single 5K @ 60Hz display running off a single cable. The official Intel slide deck says that Thunderbolt 3 supports DisplayPort 1.2 (not 1.3), but there's no mention of HDMI. The Alpine Ridge leak back in April 2014 suggested that HDMI 2.0 would be supported, but Intel today says that DisplayPort 1.2 is "the native standard" for display over Thunderbolt 3, though HDMI 2.0 monitors will be supported with an "adapter."
The same leak also suggested that Thunderbolt 3 would be paired with Skylake, Intel's next chip after Broadwell, but we can confirm that isn't the case: Thunderbolt 3 would theoretically work with Broadwell. Intel hasn't given an official release date for Thunderbolt 3, but it has told us that it will probably launch alongside Skylake. We asked Apple about its involvement with Thunderbolt 3, and a spokesperson said, "we do not talk about things that may lie ahead." (It wouldn't be surprising if the first outing of Thunderbolt 3 is with a Skylake-powered MacBook Pro in late 2015.)
At launch, there'll be one passive Thunderbolt 3 cable that supports Thunderbolt, USB 3.1, and DisplayPort 1.2, but with a max bandwidth of only 20Gbps. Intel confirms that this passive cable will be a standard, cheap USB Type-C cable. There'll also be an active cable that allows for up to 40Gbps, but drops DisplayPort 1.2 connectivity. Intel is also working on an active optical cable for Thunderbolt 3, but it isn't sharing any more details at the moment, and it won't be on the market until sometime in 2016. (Is this the rebirth of Light Peak?!)
The most exciting aspect of Thunderbolt 3 is its adoption of the USB Type-C connector. Type-C has a much smaller Z-height (about 3mm) than Mini DisplayPort (about 5mm), which in theory will allow Thunderbolt to make the jump to tablets and other small form factors. Ultra-thin laptops, such as the new MacBook with just a single USB Type-C port or Microsoft's Surface line, may also stand to gain a lot from Thunderbolt 3.
With a total bandwidth of 40Gbps, Thunderbolt 3 offers a tantalising glimpse of "one cable to rule them all." In theory, you could use Thunderbolt almost everywhere: to power your laptop, to power and drive your 4K monitor, and to power and connect all of your external peripherals. The one obvious exception is external graphics cards, with all but the lowest-end GPUs still drawing more than 100W. By supporting USB 3.1 and jumping on the Type-C connector, Thunderbolt 3 may actually be the interconnect to usher in that tidy-cable utopia.