This would be possible, requiring what would be a minor code change to the External Data APIs. (See
the wiki page about these APIs.)
When the external data feed was first enabled, this was one of the points that was raised. Tom replied that he didn't want the data about current region population to be available in this manner, as it could lead to people who use the external APIs getting some kind of OOC advantage over those who don't. It would make trend tracking via external tools very easy. Someone with enough programming skill could easily data mine the APIs to develop long-term trend data for individual realms and regions.
I am not sure whether or not this is a valid concern, but there you have it.
