I think that once they get the price of the Retina Macbook Pro to $1999, that's about as low as it's going to go for a while.
In 2006 a base Intel Macbook Pro with dedicated GPU was $1999.
In 2008 a base Unibody Macbook Pro with dedicated GPU was $1999.
Only recently has that bumped down to $1799 with Macbook Pro.
I think that a 13" Retina Macbook Pro will eventually fill the $1500-$2000 slot, with the Macbook Air below it.