[0] https://wowwiki.fandom.com/wiki/Character_Transfer
[1] https://wowwiki.fandom.com/wiki/Faction_Change_service
[0] https://wowwiki.fandom.com/wiki/Character_Transfer
[1] https://wowwiki.fandom.com/wiki/Faction_Change_service
[4] “The precursors to modern-day heirlooms were introduced in Vanilla/Classic World of Warcraft. Heirlooms up to the Wrath of the Lich King expansion were items that were sold by a specific battleground vendor. There were Warsong Gulch, Arathi Basin and Alterac Valley heirlooms.”
[2] This depends on how you mark an expansion. IMO, after the initial bug fixes are put that’s the expansion. Everything after that like 3.3.0 is it’s own separate patch.
Regarding heirlooms, they were introduced in WotLK:
"Heirlooms that increase experience and scale based on character level were introduced in the Wrath of the Lich King expansion."
The line is blurry, but I believe that a trend was definitely noticeable even in late Burning Crusade. In particular, efforts to attract a broader player base. It is unfortunately surprisingly hard to track and timestamp all the controversial changes introduced to the game.