In an update on the game's official site, StarCraft II: Heart of the Swarm developers Blizzard have outlined some changes that have been made to the sequel/expansion during the process of testing.
Most important are that a couple of units intended to be present in the final product have been cut loose. The Terran's Shredder is gone, because it "was very confusing for players as well as being something that was easily used to kill a large number of workers with little to no warning". Gone too it the Protoss' Replicant, which "was causing enemy players to not build certain unit types and was actually removing diversity from the game instead of adding diversity".
The Terran's Warhound might also get the axe, as Blizzard fears it "still feels a little too much like a small thor, which is just not new enough to give terran players new strategies".
You can read more about some of the finer tweaks at the link below.