Raids, but not in the way you described it. In the way rollin (and if you look for my post as an expansion of it, which included incorporating the Arena system) had described it (online, in an arena/small map kind of thing), that's the way it could work with Legacy. The offline thing wouldn't work as well.
The Rogues thing is also a really nice idea, but I feel the Raids System (in the original form of it as suggested, not what's written in the OP) is more open to all players (including raids specifically for newbies) as opposed to having the Rogues WL system which is purely for Rogues.