As if the reversible USB Type-C connector weren't cool enough already, cables based on the standard will be able to carry DisplayPort signals. VESA and the USB 3.0 Promoter group have worked together to implement DisplayPort via Alternate Mode, an extension in the Type-C spec that allows data lanes to be repurposed for other functions.
VESA promises "the same performance and feature capability as a standard DisplayPort connection" with support for audio and "monitor resolutions of 4K and beyond." The maximum resolution and refresh rate will depend on the implementation, though. Passive Type-C cables can have up to four lanes, all of which are available to Alternate Mode. Each lane has 10Gbps of bandwidth—plenty for not only DisplayPort 1.2a, which peaks at 5.4Gbps per lane, but also DP 1.3, which goes up to 8.1Gbps.
As one might expect, any lanes commandeered for DisplayPort can't be used to pass USB 3.1 signals. However, the Type-C spec has a dedicated USB 2.0 channel that's unaffected by Alternate Mode, ensuring a measure of all-purpose connectivity even when the main lanes are monopolized by display data. Passing DisplayPort signals doesn't affect power delivery over Type-C cables, either. The standard can supply up to 100W to connected devices.
Devices with USB Type-C connectors will need to support Alternate Mode explicitly for the DisplayPort mojo to work. Compatible hardware should be labeled clearly, though, and I'd expect cables to advertise lane counts. You might want to stick to shorter lengths, because 10Gbps transfer rates are only supported up to one meter (3.3 ft). The standard works with passive cables up to two meters (6.6 ft) long, but those can only push data at 5Gbps per lane.
The prospect of combing audio, video, data, and power on a single cable with a reversible connector is pretty sweet for both PCs and mobile devices. And everything is based on royalty-free standards that should be relatively cheap to implement. Your move, Thunderbolt.