And then there are families and titles with many competing orders of succession based on fact, suspicion, etc. Examples: Bran Stark is the legitimate Lord of Winterfell, but some argue it's Jon Snow based on Robb's will (which was based on the mistake that Bran, Rickon and Arya were dead). And then there is the royal decree naming Roose. So there are multiple possible successions there. Same obviously for the Iron Throne, the Greyjoys, etc.
A subplot here touching on previous episodes would be where and how women inherit. Bear Island, Stokeworth, Barrowton, Hornwood, and many places in Dorne serve as interesting examples.
Another subplot could be the succession to Lord of the Vale which has some interesting background, and also in the Westerlands. Technically, Cersei is now Lady of the Rock. That would mean on her death Tommen could conceivably have the Iron Throne, the Westerlands AND the Stormlands. (If he lives....not likely.)
Then there are the Freys, Tullys, and others where there are big question marks.
I could go on, I think there is a lot of stuff to discuss here and also a lot of room for speculation and arguments on all sides based on a lot of things. Legitimacy, false information, bastardy, disinheritance, being attainted by the crown, being lawfully legitimized, etc.
