Actually I thing energy consumption wont be any deal breaker regarding future world currencies. PoS will never make it big, if they would they would have done it already.
Why do you think the huge energy waste wont be a deal breaker? What will happen when all BTC are mined?
The conclusion of your second sentence doesn't follow from the premise, because your first premise is wrong imo:
P1: If a "Proof of X" currency hasn't already made it big, it never will.
P2: Proof of Stake has not made it big.
C: PoS will never make it big.
P1 was proven wrong in the past, when PoW made it big. Would you have said the same about bitcoin before it was big?
The idea is that by the time Bitcoin is mined out there would be more transactions going from a > b to sustain the amount of miners that would be staying in the game. Difficulty adjusts itself as miners leave making it more profitable