I was on the original QF76 19/10.
One of the four engine electrical generators on VH-ZNE faulted on the taxiway prior to take-off. The crew tried to troubleshoot on the ramp for a few hours, then deplaned everyone to do a full electrical reset, but ultimately they determined that the issue could only be resolved with replacement parts flown in from either LAX or SYD.
While I always want to be on the ground wanting to be in the sky, rather than in the sky wanting to be on the ground, the whole experience was not well managed. Boarding was at 8:30pm, and the crew continued to announce that they "should have it resolved within 30 minutes" for 4 hours, before being deplaned around 12:30pm. The crew were rapidly running out of duty time (less than 2 hours of buffer remaining upon deplaning - barely enough time to deplane, re-board a full 787 and taxi). They should have just called it and cancelled the flight hours earlier.
After timing out and cancelling the flight, they continued to run engine tests for another hour (hence baggage handlers could not approach the aircraft), leaving a couple of hundred passengers at the gate with no information in a closed terminal (all terminal facilities including immigration / customs were closed for the night by this time).
Qantas' externally contracted ground staff were a mess, totally disorganised and not able to communicate with the crowd.
Eventually myself and my 2-year old bailed from the airport around 4:00am to organise our own transport and hotel (they hadn't even started started organising this for the other 200+ pax by this time) and I called Qantas the next morning to be rebooked on another airline, even though they kept claiming "QF76 has been delayed but will fly later today (20/10)". We got home to Melbourne via UA before the QF7076 had taken off.
Bit of a rant, but it really showed the deficits in Qantas' customer service and disruptions handling is for non-major hub destinations in their network.