that's VERY sensitive information - in fact some of the most commercially sensitive info an airline holds I 'd have thought
Yes, I'm sure such information is not made available by the airlines. But now that I think about it, I'm kind of surprised that no enterprising person, or Tripadvisor-type entity, has made a crowdsourced app to collect and analyse such data. It would be pretty easy to make an app where pax can, during or after their flight, enter the flight number and date and click a button for "25% full", "50% full", "75% full", "sardine can", or whatever. The incentive to participate would be access to the consolidated data.