The Whale = Leviathan.
The "belly of the whale" is typically associated with the womb--specifically a second, spiritual womb--and rebirth (not birth).
I expect we'll find out that Talia hyper-aged the Damian clone and that the entire 666 universe was basically a simulation to create her perfect little monster. Or, well... I don't expect it, but it'd be cool. lol
More likely, we'll return to the genetic labs from "Batman: The Return" and learn about the facility that was responsible for the monster's creation.
I just realized that another typical association with the belly of the whale is the boat = the coffin (see Hamlet). Who was the last person we saw in a coffin? That's right:
It'd certainly be interesting if Talia rescued Hurt and became his kind of spiritual mother. It would give her access to the Hyper-Adapter, as well.
But since Morrison has played with hypertime simulations before (New X-Men, The World), I wouldn't be entirely surprised if, again, 666 was some kind of simulation for raising the clone.
lol Who knows... It'll be what it'll be. So many ways it could go.