I don't know, but using face detection to better analyse travellers seems even creepier that logging mac addresses from phones.
This has been suggested before, but the media exploded - people don't want to have visual recognition systems looking at them.
I guess it's easier to process MAC/Wifi data/numbers than faces.
I believe that some more modern trains allow TfL to measure the weight change of carriages under passenger load, which can be used to estimate numbers, but imagine the cost of trying to roll that out on all trains and platforms... The fares would have to double for a year at least.
I'm sure the Class 345s, soon to appear on Crossrail, do this to show loadings on platform screens (to trying to avoid crush loading in specific coaches while others are empty), but I can't find any source for that. The Class 700s on Thameslink show loadings on platform screens in the "Core" section, but this is based upon CO2 levels within the coaches.