I hope this is useful for those who want a maybe last chance to experience them.
Please feel free to add in a reply if I have something forgotten (quests or RP).
Burning Crusade:
- Hellfire Peninsula, Horde:
(2 Quests): https://warcraft.wiki.gg/wiki/Messenger_to_Thrall
(2 Quests): https://warcraft.wiki.gg/wiki/A_Debilitating_Sickness - Nagrand, Horde (2 Quests): https://warcraft.wiki.gg/wiki/Thrall,_Son_of_Durotan
- Race Intros and Zone-Breadcrumb quest for Draenai and Blood Elves
- Not removed, but canon version: https://warcraft.wiki.gg/wiki/Meeting_the_Orcs_(blood_elf)
- Some Dungeon quests were removed or changed (I did not researh these yet)
Wrath:
- Battle for Undercity, Alliance (5 Quests): https://warcraft.wiki.gg/wiki/Reborn_From_The_Ashes
- Battle for Undercity, Horde (4 Quests): https://warcraft.wiki.gg/wiki/Darkness_Stirs
- There is an RP event in the Undercity Apothecary after the Event
- Some Dungeon quests were removed or changed (I did not researh these yet)
Main World BC revamp:
- Western Plaguelands, Alliance (2 Quests): https://warcraft.wiki.gg/wiki/The_Mark_of_the_Lightbringer
- Western Plaguelands, Horde (2 Quests): https://warcraft.wiki.gg/wiki/The_So-Called_Mark_of_the_Lightbringer
- Hillsbrad, Alliance: https://warcraft.wiki.gg/wiki/Missing_Crystals
- Thousand Needles, Horde (3 Quests): https://warcraft.wiki.gg/wiki/A_Different_Approach_(BC_Classic)
- Badlands, Horde: https://warcraft.wiki.gg/wiki/Unclaimed_Baggage
- Hinterlands, Alliance (5 Quests):
(3 Quests): https://warcraft.wiki.gg/wiki/Featherbeard's_Endorsement
https://warcraft.wiki.gg/wiki/Preying_on_the_Predators_(The_Hinterlands)
https://warcraft.wiki.gg/wiki/A_Gesture_of_Goodwill - Swamp of Sorrow, Alliance (3 Quests):
https://warcraft.wiki.gg/wiki/Pool_of_Tears_(Alliance)
https://warcraft.wiki.gg/wiki/Mercy_for_the_Cursed
(Breadcrumb only) https://warcraft.wiki.gg/wiki/Help_Watcher_Biggs - Swamp of Sorrows, Horde: https://warcraft.wiki.gg/wiki/Little_Morsels
Cersei does have some RP: https://warcraft.wiki.gg/wiki/Cersei_Dusksinger - I did not check for other RP situations yet, just research any noteable NPC you encounter (i.e. Blood Elves or Draenai in the Main World)
- Not removed but maybe changed:
Nemeth Hawkeye (Horde) in Stranglethorn Vale (2 Quests)
Evonice Sootsmoker in Seasing Gorge (2 Quests)
Alliance NPCs in Forest Song Camp in Ashenvale (9 Quests) and Horde version of “Diabolical Plans” (3 Quests)
Duskwallow Marsh (The majority of quests were added in BC, the zone is mostly unchanged in Cata) - One questline in Duskwallow was added in BC and partially removed in Wrath (3 Quests): https://warcraft.wiki.gg/wiki/Survey_Alcaz_Island_(BC_Classic)