The actual paper cites using devices with Thunderbolt 2 ports (iMac, Mac Mini both have Thunderbolt 2 via DisplayPort) to experiment on as well. It sounds like the vulnerability is in the Thunderbolt protocol in general, not just the USB-C implementation of it.
The vulnerability applies to all DMA-capable devices (ie Thunderbolt, PCIe, wifi and NVMe chips on mobiles, on-chip peripherals like mobile basebands). Thunderbolt 3 makes drive-by attacks easier, but in principle the attack could be carried out from any DMA device (subject to practical limitations like reverse engineering of firmware). Our earlier attacks were done with PCIe and Thunderbolt 2.
USB-C Macbook Pros we’re only announced on Oct 27, 2016. Not sure what version of 10.12 they shipped with, but seems like it was a pretty fast fix.