Thunderbolt is capable of doing this, but USB has had support for peer to peer and alternative client support for quite a while. USB OTG (On-The-Go), which allows a USB client device to also act as a host, has been around since the 2.0 spec. This is what lets USB devices like phones and tablets also connect to card readers, keyboards, and other USB devices.

What Thunderbolt can do however that is quite magical, is operate as a point to point network interface. Driver support can be a bit dodgy, but it's totally feasible to build a 3 node compute cluster with point to point cluster node networking over Thunderbolt at 20 Gb/s.