Can agree and understand why 4 difficulty levels are a pain and boring for some aspects. But still, if they put act V as Inferno only that would mean:
- no new leveling character would see it before reaching level 60.
- it needs to be at least two difficulties: inferno means all monsters are cap level + 3, good luck fighting act V monsters with your level 60 char; so basically you would need act V leveling version and act V farm version at minimum.
- if act V was inferno only, that can mean only two things: a) it's the only level 70 inferno content b) they will scale all inferno to level 70. Which both are bad options since they kill the farm choices or kill the endgame for people who won't buy the exp pack.
Imho, better if act V becomes a part of the story/leveling process. Since You are already 60, you can run only act V Hell to level up to 70, than return to farm inferno - i don't think it would be a problem to check which chars have already inferno unlocked and make them go straight to Hell difficulty.