Misanthrope Prime
Hero
I play up the cyberpunk in my Eberron, so to me you're not born with a dragonmark, the house tattoos it onto you and it includes things like a tracking beacon or mind control drugs, with some lore about being tied into one particular interpretation of the draconic prophesy. It's harder to be a rambunctious "heir" but I also feel it makes it easier to make the houses villains as they can show up whenever for a fight.
