With a new Theros set about to hit, in a vacuum, the need to
exile an enchantment will be higher as new and shiny indestructible enchantment gods make their way into a large number of decks. In the short term HI may not catch on in EDH overall, but certain decks, say a gain life theme, may still want this over/in addition to
Crush Contraband, etc. The double white in the CC means, at least for me, it won't ever be competing with
Crush as I tend to use that in tri+ color decks off a splash. Maybe white based stax decks will want HI for a
Vandalblast /
By Force type effect to get the initial rush of opponent mana rocks off the board to let their strategy take hold.
As a side note, I personally haven't found a big life gain spell does that much, especially an
X spell like this, as you spend your turn gaining life [or holding up mana for end of turn cast] that usually just gets taken away [and then some] before your next turn [assuming you even get one]. Tacking it onto a mass
disenchant effect at least takes away the
opportunity cost of taking up a card slot. However, I don't see myself ever putting HI into a deck for the life gain aspect. It could make it into the deck list but the life gain likely won't be a consideration.