The raiding and in general online gaming community is leaps and bounds above what it used to be. On private servers, people have cleared MC with half or less of the players required.
Molten Core is going to get completely steamrolled, as will every other raid dungeon. Classic isn't going to be filled with people who don't understand WoW or WoW game mechanics, it's going to filled with veterans and addicts. If we go based on private servers, even Naxx is going to be cleared pretty effortlessly.