I liked that plot thread too, and it's a shame it was never followed up at the time. Short stubby people never seemed to get as much love in the game line or metaplot as slender hot elves or tieflings, or gothically angsty shades or drow...
Some stuff to think about:
Why is it called the THUNDER blessing? Dwarves largely live underground, storms don't really bother or affect them and I don't think they even have a weather god. What does thunder have to do with anything?
At the risk of overgeneralising based on your rough generation categories above, and at the risk of brushing as gently as possible against real-life stuff - could there be a degree of cultural strife post the Thunder blessing? Dwarves live a long time, and so their rulers and elders hold power for a long time. Maybe the elder generations are bing percieved as holding on too tight to the pre-Thunder ways or feeling out umbered and threatened by impulsive youth, while many younger dwarves are feeling like traditional dwarven society hasn't really got a place for them, and are exploring ?
What happens when a dwarf 'breaks the stereotypes'? How does that fit into ordered dwarven society? If you're the first dwarven wizard (for example) in your clan, how do you learn, who do you apprentice to, what guild do you join? Dwarven society has its old reliable structures, and there needs to be places for people if they want to fit in. If there aren't, either the structures have to change or people are going to get forced out.
Similarly, what about the dwarven pantheon? It's not the most varied one out there - pretty much half of it is made of some variant of battle or guardian gods. If the younger generation of dwarves are moving in large numbers beyond the Axebeard Goldminer stereotypes when it comes to lifestyle, they might not find a god that suits them among the traditional pantheon. Either the existing dwarf gods grow and change, or a lot of dwarves start worshipping non-dwarven gods, or else new dwarf gods spring up from somewhere to fill the gaps.
On a related note, where are the EVIL dwarven gods? I mean, you've got Abbathor, but he's pretty weaksauce, then the Duergar gods but they're pretty racially specific. Where's the dwarven god of excessive festering resentment and vengeance, or the dwarf god of stasis and the revering of the ancestors to the point of undead cultism, or the god of orc-hatred to the point of genocide? I kinda wondered briefly if the Thunder Twins were a sign of a second, parallel dwarven pantheon was being born, an evil pantheon as a philosophical opposition to the regular dwarven gods like the Dark Seldarine. Maybe one twin was destined to be good and one to be evil.. Or something.