> IPMI and other solutions are nice, but what I would like to have is a standard serial interface to an UEFI shell running at all times.

One thing I miss about Sun SPARC (and other Unix) systems: you had 'proper' remote access at a very low level.

I always found BIOS/UEFI remote console very fiddly and hit and miss (you often have to play with GRUB/kernel settings to get input/output).