I'm about to wrap up STK and there is just a ton of meat on the bones in terms of content that the party never saw.

I was thinking about letting them get some play time at level 11+ and have Hekaton send them after the rest of the insubordinate giant lords (only Guh was killed).  

I'm looking for ideas on:
-how to rebalance for that level
-ideas on what to add to the strongholds 
-Other ideas like going after the Kraken or Klauth
-Especially what to do with the could giants. I don't have any ideas there.

What I have so far
-Add the giants from volos for some extra power like the fire giant dreadnaught 
- Iymrith sold Harshnag to the frost gaints
- Fire gaints have assembled the vonindod construct
-One or both evil sisters transform themselves into a storm giant quintessence 

Suggestions?:
-The module suggests a stone gaint trying to raise a tarrasque to destroy the human world that has defiled the old gaint kingdom.  Maybe there is a level appropriate monster they could have raised?
-The cloud giants were looking for some dragon magic hoard, id like any idea for what this could be to throw at the party?
-Klauth encounter?