server ipmi includes serial over lan, which can work ... it's helpful if the console settings for early boot match the console settings for OS boot, and there's no standard for sharing them, so that's a bit of a mess... and then you have some where serial over lan drops out during boot, which is kind of terrible. :(
But, the devices here are geared towards people using consumer products as servers (which I do at home, not critizing), and serial console during early boot is not an option on those, and most boards don't even have a serial port anymore.
I will say, if you're presenting a usb keyboard, you might also be able to present usb storage which could be nice for booting off of.
> serial console during early boot is not an option on those
But it should be. There's really no excuse for the current state of affairs. There ought to be a standardized low level API for all this stuff. One should never need to directly attach a keyboard, mouse, and monitor in order to provision a piece of hardware.