according to boot(8) man page, 'it is possible to dispense with
the third stage altogether'. however, 'hitting a key' and specyfing
'0:ad(0,a)/boot/kernel/kernel' results in hard hang (impossible to
reboot with crtl-alt-del) at spinner (/-\|). booting '0:ad(0,a)/boot/
loader' works ok.
In this particular release this is supported, but you need
the hints for syscons and probably atkbd* to make it work.
It's possible to compile the hints statically into a kernel.