This probably isn't a game changer for you, but Apple mentioned at WWDC that Lights Out Management is coming to Mac Pros in the next release of macOS. You need a Mac Mini somewhere on the network to manage commands from the MDM to the turned off Mac Pro, so I don't know what happens if that Mac Mini is turned off, but it's a move in the right direction I guess. (I suppose it's because they don't want network to be up before the firmware on the target Macs is validated, but I'm not sure).
