There's still a lot - particularly remote management, aka iLO in HP lingo - missing for an actual hands-off environment usable for hosters.

I know it’s not exactly IPMI, but don’t those little external IP KVM modules work well enough to do remote admin of Macs?

The annoying thing is there's no ability to control power (or see system metrics) outside the chassis. With servers and desktop PCs, you can usually tap into power pins and such.