(Seriously, SMM serves either bizarre ILO features that high-end vendors like but are rarely used, or security agencies looking for a layer to hide in.)
I have an APM (ARM64) Mustang, and this takes a rather different approach, but probably not one you'll think is better. The chip advertises 8 x 64 bit cores, but there's a 9th 32 bit core which runs all the time, even when the machine is powered down (although obviously still connected to mains power). It runs a separate firmware, in its own RAM, but can access the main memory at will and invisibly to the main OS.
One way to look at this is it's brilliant that we can just put a tiny Cortex-M3 in a spare bit of silicon and have it do useful management stuff.
Most motherboard vendors also thrown stuff onto enterprise motherboards for doing things remotely. They can have issues: https://www.youtube.com/watch?v=GZeUntdObCA