Who Makes Thunderbolt 3 Compatible USB-C Headsets?
USB audio isn't very demanding in general, and the notion of licensing an expensive Thunderbolt 3 chipset to put in a headset is ridiculous. So expect USB-C headsets supporting Thunderbolt 3 compatibility to be the way to go. There's a lot of USB-C earbuds with inline microphones on the market since a lot of smartphone companies are starting to use the universal Type-C connector.
The rest of the market for larger, over-the-head style USB-C headphones and headsets with microphone is starting to take hold. But currently, the vast majority of Thunderbolt 3 compatible headsets with mic use the rectangular USB Type-A connection we're so familiar with. If you already own a USB-A style headset, a cheap USB-A to USB-C adapter is all you'll need to use it on a new Mac with Thunderbolt3 ports.