Blizzard has promised an adjustment to spell mana costs and an uptick in base mana regen, so it's possible that those changes will take away from the sting of this one. However, whether this will all work in game is probably something we won't know until we can test level 80 group and raid content and see how things go down when healers are forced to use one rank for every heal. Where it will still hurt regardless is definitely in PvP, where practices like using rank 1 Arcane Explosion to flush out a stealther or using rank 1 Viper Sting to fake out a dispeller will disappear.
There's also been some concern that, should these new totals be based on base mana, Intellect will fall out of favor as a stat, being that a larger mana pool will no longer be an unqualified good thing for most spells. However, since many classes will now have talents that convert intellect to spellpower or attack power, it likely won't fall completely out of favor (Edit: Well, that was a bit of a rookie mistake on my part. I forgot that base mana only refers to the mana pool before gear and buffs, including any mana boosts related to intellect).
Blizzard's tried to discourage downranking before, such as when they nerfed the spellpower coefficients on lower ranked spells across the board. However, it looks like they have certainly found a definite solution now. This change, should it stick, will pretty much be the death knell of the practice for most people, since almost every reason for using downranking eventually boils down to mana conservation.
Edit: Zarhym has now confirmed that this change is intended, and is meant primarily to kill downranking.
[Thanks to chaud for alerting us to this change!]