Unless I'm missing something traits can only be passed on through breeding, so your main character and special characters will always end up lacking compared to random offspring you create.  That ends up being kind of frustrating since I and I'd assume many others prefer to focus on the main and story characters over random ones.

I'd like to see some way to acquire extra traits on existing characters. Maybe either through the devour skill, it can have a chance of adding a skill from a consumed npc or give succubus/incubus class could give a chance to steal a trait they don't already have through sexual encounters. 

Nice Idea.

Maybe make an item for it.

Or make it a secondary effect of the soulstone.

Or change the soulstone effect, that the taken trait is stored in it and can be given to another one.

Just using a class may make it over powerd, but if using my idea with the soulsone the droprate should either be higher or make it craftable.