Sascha Wildner has committed Markus Pfeiffer’s port of USB4BSD to DragonFly. USB network, input , audio, and storage devices (including xhci/USB3 items) may work, though there’s no guarantee for each driver. This is added but not on by default, so see the first link for instructions on how to rebuild your kernel to use it. This will be in (but not default) the DragonFly 3.2 release.
(This is shaping up to be a much bigger release than I anticipated!)