In the default configuration with FreeBSD on the Raspberry console messages are written on the serial console.
After a "shutdown now" one cannot enter commands from a connected USB keyboard.
I tried to enable the video console but adding
to /boot/loader.conf just results in an error message from the bootloader.
does the trick!
Note that one still cannot enter input for the bootloader in the early boot stages.
I have not found a solution for that issue (probably needs different options for UBLDR), you will have to use a serial console for now.