This sort of thing has been an interest of mine for a while, too, and one thing I ran into when I fell through the world in Strat once (forget which version, it’s been a while) and exploring is that the geometry for Stratholme in EPL and Deatholme in Ghostlands would actually intersect to a pretty considerable degree if the two maps were merged, which obviously wouldn’t work very well.
It’s plainly visible on the minimap. Here’s a couple snaps I took from a site that gives the google maps treatment to Azeroth. The first is uninstanced Eastern Kingdoms and the second is player-questable Ghostlands. The absence of Stratholme is easily verified-in game by swimming around the landmass from the beach in Ghostlands.
The uninstanced version is particularly interesting to me because it looks like they started trying to reconcile the conflict between the two versions of north EK but ultimately threw in the towel. Another point of evidence that Blizz toyed with (but ultimately scrapped) revamping Quel’Thelas in Cata can be seen in the removal of the giant troll gates of Tor’Watha in Eversong.