Imagine, an alternate WoW, but instead of being set in the time of modern Azeroth, after the events of the Third war in Warcraft 3, it's set in the time of Ancient Kalimdor, at the time when the Kal'dorei Empire and Queen Azshara ruled.
Map of Ancient Kalimdor:
https://static.wikia.nocookie.net/wo...20160428235210
It would be before the Sundering, when the land was unfractured, the map would be much bigger because it would consist of all the lands that exist in current Azeroth, and all in between. The Night Elf empire covering most of it, all their different cities intact, wielding the arcane, the Moonguard would be there, there would be the various Troll tribes and conflicts on the borders, different things going on in different places, and a few others like Dwarves, Tauren, Pandaren, it would be interesting to explore the map and see how it all looks in those days.
It could be a prequal kinda thing, but would definitely be big enough to be it's own game with how big that land would actually be. There'd probably be some characters you could recognize there as well, but in their younger days. Imagine Black Rook Hold, but in it's prime instead of full of ghosts.
Nothing on the map would be in ruins, so all the ruins you see in game now would be unbroken, fully constructed still alive buildings.