Still need something for boot graphics for the BIOS, unless non-server motherboards are coming with serial redirection default enabled and nobody mentioned it.

Set it up with a temporary card and then yank it out after it's setup. You don't tend to access the BIOS that much.

I wonder if it's possible to set up the UEFI firmware by setting some EFI variables from the operating system for example by running efivar [1].

[1]: https://github.com/rhboot/efivar

I mean, why not use a server motherboard (i.e. one supporting AMT; not necessarily one that requires RDIMMs) if you're building a NAS? NASes are servers in terms of their workload. Take advantages of the features designed for server customers.

Availability and cost naturally. A big part of the appeal here is the low price point for a great spec bare-bones home server using these consumer parts.

Mostly cost. The board itself, but also server boards are often hard to find for desktop sockets, so that drives cost for the CPU as well. But, if I get a server board, maybe I'm going to get one with IPMI, and those usually have serial consoles and some limited VGA for KVM over IP too.

I could afford a $800 server project, but I'd rather spend $300.

Had no idea that would even boot. I prefer being able to just plug in a monitor but that's an interesting option.