It is expected projects like QEMU and coreboot will handle those tasks.
Seabios is also the BIOS of real computers, including the PC Engines APU: http://www.gooze.eu/apu-pc-engines-kit
And probably the 'real' BIOS of many others.
In a nutshell, there isn't really anything in SeaBIOS to password protect and so no reason for a password.
I am worried that SeaBIOS allows setting the priority of boot devices of the PC Engines APU without restriction. This allows an attacker to boot into any system using a USB sticks. Attacks with USB sticks are very common.
I have no idea what would solve this problem. A good password management with password stored in SHA-512 for sure. Encryption of BIOS data would also help. The interest of a password is that it will stop MOST attackers, but I agree not all (you can always compile SeaBIOS and replace it with a modified version).
Also, providing a password for a BIOS system is a requirement, when used in governments and administrations. French authorities recommend setting a BIOS password on any GNU/Linux computer. Even companies might be obliged sooner or later to set a BIOS password, as this is part of their contract with insurance companies.
Are there projects around to protect Seabios with password or encryption?
Kind regards, Kellogs