You could try the "Abilities and Traits Mod". Let me know what you think of it and if you have any ideas for future development.
I like the idea of dividing character histories or "classes" between three things: warfare, administration, and magic. Warfare classes are like the Warrior and the character is granted bonuses to health, attack, defense, and other fighting bonuses. Administration classes are the characters who focus on city benefits (ie. being stationed in a city) like the Administrator, Merchant, and Researchers who give cities their benefits for being stationed there. Lastly, you could have your Magic people who can cast spells and potentially be another sovereign'esq unit.
Some histories, like the General, are a bit of both schools. A General should be able to fight but they also have greater command or leadership bonuses that effect their troops which the Warrior won't have.
The problem is implementation and discovering new ways to "unlock" these abilities. Modders are somewhat limited to what they can or can't do right now.
I'd also like to note that making them more unique, versatile, useful, viable, and survivable requires us to make heroes a little stronger. I believe that the default hero bonuses and histories are somewhat lacking, weak, and doesn't make them very useful when they can be killed by a lone wolf or spider during any time in the game.
