Mages do have it, but unfortunately it's in deep Frost and connected to the Water Elemental.

Oh, my bad. In that case, I really wish they'd make it so it's easier to keep it up. Doesn't really work when it's attached to DPS specs that go in and out of vogue with every patch.

Well, to be totally accurate, the return from Imp Water Elemental is lower than replenishment (0.12% per second versus replenishment's 0.25%), and Frost has _never_ been a spec people wanted for raids - it was bad in BC, and is actually worse now, falling ~1k DPS behind basically every other mage spec in Naxx (and Frost's scaling is a lot worse than Fire/Arcane, so as gear improves, it falls farther behind).

That being why it never makes it into discussions about Replenishment ;)

Yeah, but on the up-side it does hit everyone in the raid (within 100 yards of the elemental) rather than getting applied to only a few people. It's still definitely not as good as the official replenishment, but might be worth considering for some guilds if mana is an issue.