[analog31]

Not strictly impossible, but probably difficult to the point where the FLIR sensor becomes a cheaper solution.

The visible detectors are kind of a lucky accident, that the visible spectrum is within the range that can be detected by a silicon sensor. Therefore, visible sensors are cheap and easy to make thanks to silicon IC technology. Sensors that detect IR beyond about 1 micron wavelength (the bandgap of silicon, where it becomes transparent) have to be made out of more "exotic" materials that are also more expensive. The problem might be surmountable, but fewer people want to set up and optimize "fabs" for those materials.

The problem with detecting heat with silicon is that the intensity is extremely low, and the amount of background radiation high. Getting a temperature measurement that isn't corrupted by other effects is going to be difficult.