I only want to discuss the visual spoilers cards right now, because those are the only ones confirmed, so no rumor site cards.

Conflux - Definite. Massively powerful.

Exploding Borders - Creature kill AND land search. Makes later game land search not as redundant. Could replace an existing land search spell.

Martial Coup - Frankly, it could replace any Wrath in the deck as it is better. Could replace a removal spell or a Wrath/Damnation type card, but there should definitely be a place for this card somewhere.

Nicol Bolas, Planeswalker - Duh.

Meglonoth - It's very big and very useful. Could replace one of the 4/4s for 4 mana, or replace another critter. Not sure though.

Magister Sphinx - Could replace one of the bigger flyers if life gain gets out of hand at hte table. Answer to Invincible Hymn (which I pulled out of my deck,. but others play).