Either Charles, Duke of Calabria or Hugh of Burgundy...Oh I just think that they shouldn't be discounted as completely lacking support. Any changes to the succession will impact their claims too, even if those claims are lesser.
Now that's interesting. Who are you currently thinking is best placed to be Isabella's husband TTL?
Philip of Burgundy (Mahaut’s son) is five years younger than her, Odo of BurgIndy would NOT be taken in consideration while his older brother live, Robert of Artois is quite landless, John III of Brabant again is five years younger than Isabella, Philip of Valois would bring no advantage and the Evreux were not of the right age (her half-uncle too old for her, his son way too young)