Hi Matt, we chated about kexec booting chromeos for Acer C710 on IRC, thanks a lot for your help.
I digged to into depthcharge code, and found they did quite a lot of work, including patching the SMBIOS for fwid, redirecting ehci to xhci, etc. However, SeaBios on RW_LEGACY can not enjoy these work as legacy mode got started very early. In addition, flash seabios/tianocore on ssd (pretending to be linux kernel) would be much safer option.