Honestly, this thread sits on a flawed premise.
Blizzard has always, ALWAYS said that one of their core values was “gameplay first”, meaning that the game is designed, and then the lore and the story are written to justify the gameplay. They have a twelve-foot tall bronze statue of a Warcraft orc riding a wolf with a plaque written “Gameplay First”, among other plaques for their other core values.
So the idea that lore will stop anything from happening is… just not Blizzard.
If Blizzard wants Undead Paladins, they will add Undead Paladins, and then they will write the lore to justify Undead Paladins, like they did with Lightforged Draenei Warlocks and what-not.