Softie;
We are talking about a simple mod, involving a simple thermocouple and a connecting wire to a display. It could have been installed during the pipe replacement programme. Complex equipment was fitted to the aircraft, in double quick time, for opertions in Afgahistan.
I think you, and others, are missing the point regarding the need for this mod in the interest of flight safety. Yes, we all know that the cross-feed is de-selected in flght, but we do not know what the residual temp is after a ground start. Data has been collected, but not reported on. Also, in the event of "leaking" cross-feed valves in flight, the ducting will rise in temp without the crew knowing.
DV