So far it seems likely. I can kinda see what PHB IV might have in stone (Shadow and Elemental classes?), but I don't know about DMG III or IV. And I don't know what could come after that. But assuming it has the quality of a PHB 2, I think I am in until I get tired of the system itself and have found a decent alternative. Which you'll never know when that will happen.I doubt WotC would publish a book unless they felt it was good and saleable, so the question for those with that discerning caveat might require a bit of conjecture in regard to how much they are likely to find to their own personal tastes.