I was recently thinking about how much GRRM has decimated most of the Great Houses.
Arryns: Jon was the Hand. All that remains is a sickly psychotic child.
Baratheon: Unless Mrs Stannis can make a male baby, this house is extinct the day Stannis dies. Which could be soon. Last surviving fake Baratheon is unlikely to survive the story alive and/or still considered a Baratheon.
Lannister: Tywin is dead. Kevan is dead. Jaime is uninterested. Tyrion is done as a Lannister. Tommen won't ever be a true Lannister. Kevan's 3rd son Martyn is the leading candidate to take control of the House down the road. He's still a child.
Stark: Ned dead. Rob dead. Bran done as a Stark. Rickon MIA. Sansa is a Lannister. Arya is done as a Stark. Jon is done as a Stark. Unless Rickon reappears, this house is done.
Greyjoy: Balon is dead. Theon is done being a Greyjoy. Family now run by a pirate.
Tully: Hoster is dead. Edmure is a captive. The Blackfish is a fugitive. The Blackfish isn't a breeder. If Edmure's wife births a son, they have a chance to recover.
Tyrell: the only house that has remained completely intact (if you believe Loras is okay).
Martell: Doran survives but his first heir is dead. Doran's brother is dead. Youngest heir still lives.
So, of the 8 Great Houses at the start of GOT, only 2 remain strong. The Lannisters survive, but the elder leadership is wiped out. They won't survive the revelation of incest. The rest of the Houses are already exiled, extinct, or nearing extinction.
I don't think it is a coincidence that the only houses the Targaryens can 100% count on are the 2 most powerful Houses as we await WoW.
And, I think Margaery weds Aegon. Of course, he doesn't survive long thereafter.
And, the dragonriders are Jon (R+L=J) and Aerys' surviving children, Dany and Tyrion.