I don't think there was ever an "in kind" rule that is that narrow. I remember back in 1999 during the Kosovo war, NATO bombed the Yugoslavian Ministry of Defense, for example - and it was generally considered a legitimate target, even though the people inside weren't directly shooting at anybody.
I think the broader context is important here. A cyber attack by itself does not justify this sort of response. But a cyber attack that is intended to bolster one side in a military conflict, carried out by people explicitly aligned with that side, is a part of the broader war effort. Responding to that with deadly force is still responding "in kind".
I think the broader context is important here. A cyber attack by itself does not justify this sort of response. But a cyber attack that is intended to bolster one side in a military conflict, carried out by people explicitly aligned with that side, is a part of the broader war effort. Responding to that with deadly force is still responding "in kind".