I like full art eldrazi cards as much as the other guy, but with Death Rattle gone from the Progenitus deck, Not of This World isn't worth the slot.

The deck needed more removal. I like adding a 3rd Traitorous Instincts into the mix. That's the choice for now. I also like the idea of a 3rd Rapacious One.

I like the cost and effect of Heat Ray, but it being a card that shows an eldrazi getting burnt has bugged me. Heat Ray also always felt to me like a card that would be more than a 1-of (but in this deck it was). I came up with several substitutes, and I think at the moment I like Roar of the Crowd most.

I wanted to avoid giving the Eldrazi deck direct burn spells that target players, because I didn't want it to win out of nowhere like that, and wanted to leave that sudden burn/life-loss trait as a strength of the Progenitus deck. But I think this card makes the exception, on similar grounds to the Raid Bombardment. The opponent sees your board.
It's not unconditional and it isn't always efficient. I like it. Extra bonus for it being a tool in the Emrakul toolbox to help knock out an Empyrial Archangel.

Summary:

Not of This World -> Traitorous Instincts

Heat Ray -> Roar of the Crowd