Chalice at 1 >>>> Pithing Needle. Chalice cripples so many decks that I would never cut it. So playing 1cc cards is not an option imo. Wasteland is not that big a threat here. Getting a land blown up isn't the end of the world when the deck is playing 27 land every one of which taps for 2 mana with the exception of Glimmerpost.
I made a decision regarding the 3 flex slots. Here is my current build...
4 Eldrazi Temple
4 Ancient Tomb
4 Cloudpost
3 Glimmerpost
3 Eye of Ugin
3 City of Traitors
3 Crystal Vein
1 Vesuva
1 Thespian's Stage
4 Endless One
4 Thought-Knot Seer
4 Reality Smasher
4 Kozilek's Channeler
4 Conduit of Ruin
4 Chalice of the Void
3 Trinisphere
2 Endbringer
1 Eldrazi Mimic
1 Ulamog's Crusher
1 Void Winnower
1 Kozilek, Butcher of Truth
1 Ulamog, the Ceaseless Hunger
I absolutely love how this list is performing.