Wrathion was an upstart, who felt that he deserved to lead. However I don’t see Dagran as an upstart. Furthermore unlike Wrathion, Dagran has the legal claim to rulership. He is the heir of both the Bronzebeard and Dark Iron clans and the Council of Three Hammers is a regency that is meant to dissolve when he comes of age to rule. Though exactly where this will leave the Wildhammer is uncertain.
Now could Dagran abdicate? It’s possible, but it’s also possible that instead of the Council of Three Hammers dissolving, Dagran will decide to retain them as his personal advisors. We just don’t know how Blizzard plans on developing his story.