Both legacy and modern image-tools have GRUB support for RS232 serial adapters, and there is console support for USB-USB serial converters as provided in configuration mode ['system', 'console', 'device']. However, support for USB-USB boot console type ttyUSB is unused (but for one notice in T5458); not very useful (see below); and has been broken since early days of the legacy image-tools.
A lasting bug in the legacy image tools resulted in a boot menu option of console type ttyUSB on a new install, but not after 'add image'. Secondly, even when available, no boot messages would be shown without addition of kernel config setting:
CONFIG_USB_SERIAL=y
CONFIG_USB_SERIAL_CONSOLE=y
and supporting modules in initramfs (for example, ftdi_sio). So, when available, it provided nothing that is not already available simply be being configured as a system console.
Moreover, even were boot messages to be enabled as above, access to the GRUB menu is unlikely, despite existing GRUB modules usbserial_*; BIOS access not available.
Given the above, one can always use a ttyUSB console after a simple configuration, but as a boot console it will be removed as an option.