Hell they could just make a Eurika from FF14 in this what adds nothing but an awesome look armor set with 0 stat increases and the people go bananas in that shit for months.
Just off scrapped vanilla zones with actual files you got Gillijim's Isle south of STV, Emerald Dream behind the dragon portals, Gilneas, The Dragon isles, Inverted Karazhan, Stormwind Vault dungeon, Grim Batol, actual Ashzara content including its scrapped battleground, Tel Abim, the prototype outland that was a rough Hellfire Peninsula that could be used as a raid, the original plan for Gnomergon, Zul'Dare off the Plaguelands, subterranian Hyjal that shows the Old Gods influence, whatever they want with the Caverns of Time, and the Underdark, which was supposed to span under the EK that was all Nerubian.