Snape's own thoughts had been tending in that direction since James' initial objections - he'd still been used to thinking of the Manor as the Malfoys' private home, instead of what it currently was: the residence of the Minister of Magic.
"It's possible the castle will need to offer sanctuary to more than the Order and their relations," he mused aloud. "Classes will be cancelled of course, and if Riddle manages to get a solid grip on power, he'll want to purge wizarding society of Muggleborns. The castle is the only stronghold large enough to accommodate such numbers." His tone of voice was abstracted, his gaze distant: clearly most of his attention was already on the details of defensive logistics.
"I wonder if, between all of us, and Grindelwald, and your father," a nod to James, "we could raise enough power for a castle-wide Fidelius."