Aside from the “if properly maintained” carve-out(hardly unique to knob and tube; but never something one likes to see, especially in comments about the safety of environments that don’t have well-regulated maintenance specialists); what makes me nervous about knob and tube is how many present day install procedures(for things like data cabling) are performed on the assumption that the interior of the wall is full of nuisance dust and fiberglass but otherwise benign; and as long as you don’t breach too many fire barriers it’s probably OK.
Wouldn’t matter so much if running fiber; but wouldn’t want data-copper nuzzling up to power if it can be avoided.
