I like Timothy Zahn's comment about family, actually. Family has been one of the biggest themes of Star Wars as a film series (given its sometimes almost myopic obsession with the Skywalker clan), but it's mostly been presented dysfunctionally, as he says.
And having Luke be the Obi-Wan to his actual child (or children) would be pretty interesting. Not to mention Aunt Leia and Uncle Han. It'd be funny to have at least one scene of those two in their understated old age shoving their kids out the front door for adventure.