Direct USB-to-USB networking? Is there an existent method, a driver, or some software that facilitates direct USB-to-USB networking in macOS similar to FireWire-to-Firewire ethernet or the new Thunderbolt-to-Thunderbolt ethernet networking?
Yes and no. Because of the host-slave relationship USB is built around this requires specific hardware, namely an active cable with electronics. They're cheap enough though, you can get them on Amazon or similar for ~$10 and up.

Just search for "usb bridge cable".