Expanding Death Knights and Warlocks was and always will be a mistake.
Paladins, Shamans and Druids are unique classes based in the culture that had formed around certain section(s) of Warcraft’s societies.
The aforementioned classes spreading to further races does not make sense and dilutes the universe’s established lore, setting and identity.
You don’t simply pick up Druidism, Shamanism, or being a Paladin. [The same goes for being a Death Knight or Warlock, but they have already dumped on that].
In the case of Druidism, you need to make pacts with the spirits of the land and animals in order to use the abilities of a Druid; and you need to be a defender/advocate for these supernatural forces (unless you’re enslaving them). Doesn’t make sense for Blood Elves, Vulpera, Dwarves, Goblins, Humans, etc to have these abilities or access to them as they are in no way, shape or form carrying out the duties associated with Druidism.
Let’s go with the best place for it in lore–Night Elves and Tauren. These were people(s) who had based their entire culture around living WITH the land and animals, not dominating/subjugating it as every other society in Warcraft does.
In the case of Shamanism, these are people who further the interests of Elemental forces/spirits. They are similar to Druids, but not quite the same. Typically these are people who were nomadic, living in huts, caves, etc. You cannot wield elemental power(s) without making deal(s) with Elemental spirits, having their respect, etc. You have to be in tune with the natural world which is not something that Blood Elves, Humans, Undead, Gnomes, etc are accustomed to. In the case of Goblins, which is and always will be a mistake, they made a literal deal with the Elements.
Now for Paladins, this is the one that has the most plausibility for expanding…as Blizzard has not landed on a specific identity for what the Paladin represents. We used to think of it as Humans and Dwarves, who discovering the Light, wielded it with great fervor during the Second War and Third War. Paladins were originally created as a response to counter the tides of darkness the Orcs had wrought with Warlocks who wielded Shadow powers. If we stick with the original identity of the Paladin–it was as pure as this:
A righteous warrior who is infused and blessed by the Light.
An identity which was not fitting for Blood Elves, Orcs, Undead, Tauren, Trolls, etc
Which is why later in the Warcraft universe they expanded it to include other forces of ‘Light’. For Blood Elves it was an enslaved Naaru(who was later turned into the power core of the Sunwell, and Liadrin’s forces had defected and converted, learning to draw on the Sunwell much the same way they had before) For Tauren it was An’she, the literal sun and a force of Nature, for Zandalari it was the Loa, etc. Paladins, and the Light as a force of magic, has compeltely lost it’s identity since the time of WotLK.
