I've been playing with the idea of replacing two kird apes with two "genju of the spires".

1.  It fits the mana curve pretty well.
2.  With burn in the deck, there arent often many blockers, and it will often be able to get through to deal 6 dmg.
3.  What about having it in the SB?  Against Combo and control, it can provide a much faster clock without taking out any of the deck's disruption. 
4.  Its not card disadvantage, because it goes back to your hand if your mountain dies.

I'll gonna keep testing this.  The only thing that holds it back a bit is paying the 2 mana every turn.

In my opinion, the 4 Root Maze is what makes the deck viable.  Root Maze is a powerhouse against almost any deck out there, and dropping one down early in the game often means the difference between a win or a loss.  I realize that drawing a second Root Maze is a completely dead card, but having 4 to have the consistency in the deck I believe is more important.  Plus, in my build I run 2-3 wild mongrels to get rid of dead cards like second Root Mazes.

I also agree with Tim that consistency in this deck is more important than draw.  In this build, the chain lightning is more important.  The extra burn can mean a faster clock and a more aggressive deck, but more importantly it can assure that dangerous little creatures such as Welder are always taken care of.

Crucible and Root Maze IS a pretty wicked lock, and I'll look into my deck to toy with it a bit, but I just don't see what I could cut to include it.