Creatures of The Far Realm would be a fun thing to base a story around. If we assume most aberrations are from the Far Realm initially, it raises a lot of interesting questions. Namely, for beings that came from a place of incomprehensible madness, they're remarkably well-adapted to our universe. Mind flayers must prey on creatures with a very human or at least terrestrial biology, so they must have come into being in response to the discovery of creatures with brains. Why is the Far Realm so much better at adapting to our world, when the merest glimpse of theirs drives us insane? It's really concerning. Is the Far Realm actively trying to "infect" our own realm?
...actually, didn't 4th edition bring up the concept that the Far Realm is a disease, and psionics is our realm's cure? That was a cool idea.