We're losing Azeroth world-building, lore development behind most playable races, the usability of those places when it fits current expansion lore, all the stuff that happened in books and on ingame texts since Cataclysm, possible new battlegrounds, new incursions from old enemies, new NPC factions, new cities/villages, old enemy factions like Scarlet Crusade/Scourge/Twilight Hammer/Bloodsail Buccaneers/Grimtotem/ and even the Burning Legion.
You fail to see how good would be to see smalls hubs of every playable race spread across Kalimdor and Eastern Kingdoms, Vulpera caravans in the Barrens to Tanaris, Gadgetzan revamped into a neutral city, Nightborne settlement in Azshara, Mag'har Iron Horde machinery, Gilneas as a city, a new World Tree for Night Elves, Lordaeron city as the main hub for the Forsaken, Quel'thalas restored, Exodar rebuilt as a proper Draenei city, Draenei/Lightforged machinery, Alterac Mountain and its kingdom rebuilt as a new hostile zone, Plaguelands cleansed, new Zandalari harbors in Kalimdor and Eastern Kingdoms, Drust incursions in Duskwood, feral Worgen in Kalimdor, Pandaren farms in Westfall and the Barrens, Void Elf hubs replacing the old High Elf ones, Kul'tirans taking control of Southshore/Menethil Harbor, Highmountain settlements in Stonetalon Peak/Mount Hyjal, Gnomeragan restored with the help of Mechagnomes, Arakkoa/Ethereals in Azeroth.
The list goes on, it's a shame that instead of a World Revamp we'll keep going to alien places such as Zerethi Mortis, while a vast and majestic world rots with the lack of creativity from Blizzard.
Not to mention that
everything I suggested above already has assets ready to use from recent expansions, unlike a new expansion where they need to make nearly everything from scratch.
The problem will not start again anytime soon if they make an evergreen revamp, bringing the world back to Vanilla standards with local threats and lore about the zone instead of a major threat destroying everything. Not to mention the graphical revamp. WoW hasn't changed much graphically speaking since Mists of Pandaria (
2012). Look at this comparison:
A revamp now, graphically speaking, would last until the game's shutdown.
This time around they need to make the revamped zones the end-game zones and only add new raids and dungeons on top of it, Cataclysm failed because Blizzard revamped thousands of quests, many old zones, and on top of that, five completely new zones with hundreds of new quests.