Since version 2.00 memtest86+ has supported adding the "console=" option to the boot loader to make it possible to have the output over a serial interface. Why do not we document that instead of having a USE-flag changing the default? And why do we not change the /etc/grub.d/ file for memtest86+ to make use of it as well, adding the option to grub.conf to boot over serial, so you may choose at boot time what you want?
sounds like a good idea!