When Episode VII comes out, Star Wars may initiate a new genre trend: The expanded universe reboot.
I just blew my mind.
Oh, that's not new. Pocket Books had an evolving internovel continuity in its Star Trek
tie-ins in the 1980s, but when TNG came along, that continuity was abandoned. For a decade or so thereafter, the books had to limit themselves to standalone tales, but starting around the turn of the millennium, a new novel continuity began to emerge and continues to this day.
You could also make a case for the separate continuities of the various Trek comic-book tie-ins from various different companies.
Then there's Stargate
's three distinct tie-in continuities -- the Bill McCay novels based on the movie continuity, the smattering of Ashley McConnell novels based on SG-1, and the current Fandemonium Books continuity that ignores the others.