Hi JammedStab,
I don't think this is the same as the wakeup that's on the 777. The wakeup on the 777 will actually activate even if the A/T is disengaged (blank FMA) via the throttle switches. Let's say you are level in |SPD|HDG SEL|ALT| at 6,000' and you disengage the A/T and manually reduce power. On the 777, the A/T will actually wakeup and activate in SPD mode to keep you from stalling. I don't think the -400 will do this.
The activation on a VNAV PTH descent when you get slow while in HOLD is different. That happens on both the 744 and 777.
It sounds like the 747-8 does have the wakeup feature like the 777.