The USB 3.0 promoter group announced it's working on a new power delivery specification that will enable higher voltage and current in order to deliver up to 100W of power via the USB interface:
The USB 3.0 Promoter Group is announcing that it is creating a new power delivery specification which will significantly extend the capabilities and usages of cable bus power in USB applications. The new specification will enable delivery of more power via the familiar USB connectors and cables, and will coexist with the USB Battery Charging 1.2 specification and existing USB bus-powered applications.

Key characteristics of the forthcoming USB Power Delivery solution include:

• Compatible with existing cables and connectors
• Enables voltage and current values to be negotiated over the USB power pins
• Enables higher voltage and current in order to deliver power up to 100W
• Switchable source of power delivery without changing cable direction
• Coexists with USB Battery Charging 1.2 and works equally well with both USB 2.0 and USB 3.0