I say that if we have class exclusiveness with racial traits it should allow for justifiable reasons to play any class no matter the race, in addition, allowing a race to be one class makes no impact if players don't pick it, for example, if we have orcs able to pick warrior and mage, most people will pick warrior before piking mage but the option for those who want to play an orc mage is still there, so, 76% of orcs play warrior and 24% play mage. the only thing we could expect to make it some more lore wise it will be that trainers for mage or any other magical class will only be set on undead npcs at their capital so it will make sense that for an orc to learn new spell and complete class quest they travel to the undead capital in order to learn them.
Yes i agree they have to be justified through lore, and Scars of Honor is creating a new universe from zero so they can do it in a WISE way, if they do it well of course.
I would prefer each race having their own version of each class. Like Orcs warrior being different from human warriors, Undead Paladins being different from Infernal demons Paladins, with similar skills but adapted to the race personality.
That's a lot of work, but I don't think it can happen, so I'm gonna give all the possible understandable reasons they can implement to make the Undead Druids and Undead Paladins possible.