Its a great undertaking indeed, but it would be a massive addition to the private server community. Indeed it is a massive amount of work, and there's a lot of those out there that speak about it as if its little and learn later, but those of us who have worked on large changes like that know how to get the work done, having a leader that knows the odd ends of everything is also extremely important, if the leader is lacking knowledge in any area its harder for them to correctly identify what it is that they wish to change. But make no mistake, a full remake of the game is doable, what the private server core doesn't code, blizzard provides in the client end of the game. Having a diverse team with various abilities is the key to success in this... the problem is also with the workforce, how long will someone work for a project that they wont see a cash return on? just as long as the inspiration from the leader fails.

There are alot of things that go into such a project, not just the world, but the social and psychological effects as well. But great leaps in the gaming industry are usually brought about by the smaller groups and companies. When going into a project like this, its important to know that while there is no cash equiv that you will receive for the work, there is the change, however remote, that your efforts could be noticed by a developer in the field. This is why I do large projects, because the small ones will never receive enough acclaim to stir up the attention of the big wigs, and I salute those that are willing to do the same.

What you must ask yourself, is if you're truly wanting for something like this to come around, who must you find to help you get to that point, what it is that must be done, and what are the skills required. If a forum community of even slightly skilled people rallied behind one person and worked on a large project like this one or mine, then the project would be completed, and we would have an entirely new direction to take our present and future developers.
With new jumps like a huge expansion or mod like these, so too will come guides and developer tools, making it easier for the next person to learn and do, and then the next generation will benefit from that generation, and on and on until it becomes as common as the original core.
While it is true that custom content is looked at in reserve, many want to find it to be exciting. The trick is for the developers to find a desire that has been lost, and place it back in. To make the old new again. If you can find that, and provide a world that can take advantage of it, then you really got something.