IMHO the Replenishment argument of how Frost will become more viable than it is now is non-existent. If you look closely at the changes, they can be considered a downgrade to the Frost Mage's utility as opposed to some buff to the tree.
While the actually effect of the Improved Water Elemental is only half a strong (.12%TM as opposed to Replenishment's .25%TM), it does currently stack with other Replenishment effects - of which Anobix has stated many classes do grant. Furthermore, the IWE Talent can be strategically used to last 2 Straight minutes for intense fights, or in fights lasting 5 Minutes can be busted immediately, then again for 2 straight minutes at the end. The control and reliability of this current effect is powerful in its own right.
A synergized 25-Man Raid currently does not go without a Retribution Paladin and a Shadow Priest anyways - it's too much benefit to DPS PAST the Replenishment effect. Really, this then should not be a problem. This means that every 8 seconds, 20 people are getting a 15-second replenishment effect. Theoretically, and of course never perfectly executed, this means that the entire raid should have Replenishment up almost all of the time while engaged with only *2* players. It only takes 1 of these to keep a 10-Man completely replenished the entirety of a fight. The beauty of this is that these classes are support DPS classes (aka not Warlock/Mage/Hunter/Rogue) and that, ontop of being notably strong damage dealers, are intended to bring something extra to the raid - which they do (in multiple ways.)
Now add in Survival Hunters, who not only bring pure DPS, but also bring multiple benefits to the raid. Very few a'raids amass 25 people and have 0 Hunters. So, tell me why we should have another pure DPS class choose fall way behind on his/her primary role and strength, in order to compete - nay make obsolete - these 3 sources of Replenishment. In addition, where Affliction is getting a dumbing-down and a slight Nerf, Destruction Warlocks have the ability to spec into Replenishment as well (similar to Survival's effect.)
It has become relatively obvious that Frost will continue to be neglected as a viable Raid DPS option - at least for 3.1 release - and the Utility she brings is the only plus side. So why, oh why, would changing a controlled Mana Regeneration effect that stacks with current effects into an effect that completely nullifies other classes' benefits (but in actuality provides 0 benefit because the effect will be up nearly 100% of the time anyways) be considered an upgrade to the spec??
(It's not... it's not at all.)