It seems like a nice idea, but there's always the issue of how will SE handle those achievements when they come out with new classes. For instance, you get the Warmonger title for the achievement "Mastering War'. When Rogue is released, will this be removed from people until they level the new class up? Will it be added to the achievement only for people who have yet to earn it? Or will it not credit towards that title at all? etc

Although I'd be up for a special title for mastering all DoW,DoM,DoL,and DoH