I don't claim the following as fact, but my perspective/thoughts on the topic.

You're never going to go to a happy balance where everyone has instant queues, because people largely like hitting things with big numbers more then they like healing or taking hits. NPCs are always going to be dumb to the point where they would have to dumb the dungeons down to an equal and accommodating level. Let's assume that the second point isn't the case, if they make an efficient NPC, people will be less inclined to play with real players in a so-called multiplayer game save for in content that bars this feature.

About the only place where I can think of this being helpful, is if people stopped running old content/dungeons, but the roulette system handles this well enough in my opinion. I'd disagree with it for current content, it's a multiplayer game, play with people and not robots. You can run a dungeon with all DPS though you aren't likely to get very far in most cases, and I don't imagine there is a big enough outcry of people wanting this to warrant an entire automated dungeon balancing system being implemented to accommodate when a non-standard party enters a dungeon.