With still no re-opening date and all this (no doubt preplanned) night / weekend work coming up, I almost suspect they are trying to get the line electrified earlier than planned (sacrificing the reopening date), possible because of the state election in March.That could be a possibility, but I would substitute the words "with lateness measured in weeks instead of months" where you've written "earlier than planned."
We know that not all of the upcoming night works affecting the Belair line (i.e. the Adelaide-Goodwood part of things) are pre-planned, the department has acknowledged that some of the gantries have been placed incorrectly and need an extra closure to be relocated.