It shocked me for a second -- not only is this dumbing down the questing game even further (maybe someday we will have a large red arrow pointing out a quest target from zones away), but it seems to be an awfully big break in immersion. Blizzard is basically telling you that "this is the mob you need, right here," and actually reading the quest text becomes even less necessary.
But then I realized that tooltips themselves aren't exactly paragons of game immersion -- it's already a little jump in the reality of the game to see a box with a mob's name and level whenever you mouse over it. Tooltips are already where the UI meets the road, so to speak. And as for the "dumbing down" of the game, most experienced players already had this functionality through addons like Questhelper and MonkeyQuest anyway (and if you do plan to complain that this makes things way too easy, make sure Questhelper is out of your Addon directory before you start typing). But if the tips stay in the game when the patch goes live, questing will be that much easier for people who stick to the basic UI.