I don't like it. I don't think a future Complete Divine (-like product) would serve the players of Eberron as well as Faiths of Eberron. I don't think writing Faiths of Eberron to be appealing to players in FR would make the book better for players of Eberron. And so on. By trying to dance in all weddings, WotC will create so-so products that don't really serve well any one setting.
Can I take the Red Wizard and apply it to my Birthright game? Sure. But I would be better served by a Wizards of Anduria book, and the guy playing FR would be better served by a Red Wizards of Thay book than by a Red Wizard class in the Arcane Power book. By producing the Arcane Power book, WotC provides a so-so gaming experience to both of us; if they produced The Red Wizards of Thay, they would make a better game experience for the guy playing FR, and the guy playing Birthright could harvest ideas and mechanics from it about as well as it could from the generic Arcane Power book.
I don't think you can do both generic and setting specific. Well, you can't do it well.
As for settings, I'd love to see a new Birthright. But I doubt it. Birthright (like Darksun) appears to be too restrictive, i.e. not generic enough for WotC's new philosophy - you can't use much of the core (or, supposedly, expansions) material (certain races and classes in Darksun, for example, with their associated feats, paragon paths, and so on). Birthright is also far, far less common in popularity polls.
My bet is that after FR and Eberron, we'll see Planescape/Spelljammer, followed by Ravenloft. A new 4e-based setting is possible at any point too.
