I successfully installed OpenBSD 6 on a system that only has USB console by broadly following the instructions here http://unix.stackexchange.com/questions/292891/how-can-i-install-openbsd-using-the-serial-console-without-external-monitor-wi
When the console cable session is connected, the system boots up fine, no problems. When the console cable is disconnected, the system seems to hang somewhere, and then once I re-connect to the console the boot process continues fine. I'm obviously unable to tell at which point the boot hangs because of the need to press the return key a few times to get the initial console response. (During the install process, OpenBSD prompted whether I wanted default console set to tty0 and I said yes).
