QNH by definition is “barometric pressure measured at sea level, corrected for the elevation of an airport”.
ICAO defines it as "Altimeter subscale setting to obtain elevation when on ground."
Question for pilots: are you guys going to use barometric altimeter in full IMC, say WX at minima, flying ILS CAT 1 to the minima of 200 feet?
It's a reasonable question to ask, but the answer is yes, we would and have done so for decades.
For the impact of temperature error, precision approaches with a glideslope independent of the altimeter are, in many ways, less critical than non-precision approaches where the altimeter is the only measure of level. A low DH is probably less important to correct than for example the FAF height. As an example, on an ISA-20 degC day, an indicated height of 1500 ft will actually be about 220 ft lower than that, a true altitude of less than 1300 ft. That's a substantial proportion of your 492 ft obstacle clearance before the FAF and 246 ft obstacle clearance after it.