I feel like there's a lot of discussion over things like RDF and "should we have cata classic or not" and not enough over things that would actually make wrath (and maybe even the end of TBC) better. I also think that blizzard has much more capability/infrastructure to implement these changes compared to private servers.
These are mainly things that I think would make the game better for a large majority of people without changing the game much, not including WotLK Classic gold, Items, and so on. Some of them are from private servers and some are just ideas I came up with.
-WINTERGRASP BATTLEGROUND BOARD - that shows - kills, assists, damage and vehicle damage done, rocket strike dmg done, vehicles/towers destroyed, etc.
-MULTIBOXERS IN WINTERGRASP - think about ways to limit multiboxers in wintergrasp - some private servers just ban them but when you see literally 20 boomkins press starfall to delete every vehicle and rejuv/wild growth themselves its just unbeatable. I'm not sure what the right decision here is but I'm sure someone's thought of it.
-TOTEM-left clicking your totem on portrait targets your totem.
-RAID MARKER - being able to raid mark the floor like in cataclysm (and able to keybind them) - smoke flares are basically same thing but worse.
-PROFESSIONS - crafts giving +3 and +5 instead of standard +1 for everything like in cata (crafting big item is +5 etc) - this is a big change and probably the most controversial but I think the system is cool and makes sense that crafting lvl80 epic spellweave gloves is +3 or +5 skills whereas crafting some random green item would only be +1.
-TALENTS/CURRENT BUFFS - have it update on the "character info" tab - warlocks's 3% suppression talent, even the enhance tree doesn't specify what type of hit rating it increases and can be confusing, have 5% spell haste totem and procs like eradication update as well etc.
-MENU CHANGES - toggle-able thing in the menu that allows you to see target's current armor, fire resist, health, attack power etc in the bottom right corner like when you hover over a player (maybe there's an addon for this but idk) just helps to see if someone in ur raid dropped sunders or demo shout etc.