The specification for USB SuperSpeed is getting a significant overhaul to a point that it would probably make Thunderbolt hardware pointless for a lot of people. As of now, Thunderbolt v2 has 2 main advantages over USB v3.1 SuperSpeed+. Throughput where USB 3.1 gives 10Gbps and Thunderbolt v2 providing 20Gbps- and power where USB 3.1 allows up to 4.5 watts, whereas Thunderbolt v2 allows up to 10 watts.
In the meantime, the upcoming USB type-C connector will also be receiving improvements as reported earlier, such as reversible connector and a robust cable which can provide up to 100 watts.
The Type-C specification is expected to be completed in July, whereas the 100 watts capable cables are expected in 2015. The 100 watts USB cable will be useful, as it can support powering up an external storage drive and a 4K display. However, its another part of the story that Thunderbolt spec may get overhauled by the time USB can match with Thunderbolt v2.