Well this is no official, but rendering above published by CAR magazine is showing that Mercedes is planing a new Crossover, smaller than GLK, and in direct competition with Audi Q3 and upcoming BMW X1. This resembles a B-class, and its name, BLK suggests that it would be the big member of Mercedes small cars family A and B class.
source : CAR
It appears to be a downsizwd GLK. It would probably be perfect for a small family.