Eldrazi's Chalice of the Void locks out our cheap spells at a set mana value, so we want backup lines that don't all funnel through the same cost; Empty the Warrens and Galvanic Relay as storm-based backup win conditions give Burning Wish more flexible targets at different mana values. Song of Creation and Gaea's Will are both high-risk, high-reward engine pieces that do little if Chalice is set on 0 or 1 and we can't chain cheap spells, so they come out. Watch for Thought-Knot Seer stripping our hand before we can combo off, and try to combo before Chalice of the Void resolves if possible.