It's incredibly hard for new MMOs to compete with established ones. I would think it's nearly impossible.

A game that has had 10+ years of development and content already released offers far more to a new player than most other MMOs available. A company can either release it early, with the basic core elements and a 'playable' game, or they can develop it for several more years to make it more appealing.

Honestly though, the trend lately has been to release betas/early versions of the game, and I'm not entirely sure SE made a bad decision by releasing the game as it was. At least from a player's perspective. It's doubtful that if the game had not been released, as many changes and fixes would have taken place, and it is likely there would have been no player polls to help guide development.

Whether it was a financial mistake or not... in the end, MMOs are only successful several years from their release, and they are successful based on whether the game is good or not. My opinion is, the early release and the additional feedback from the players will contribute to a better game.

I have never thought anything WoW has done was revolutionary at all. I played it for some time, but without my friends playing, I instantly quit. There's nothing spectacular about the gameplay or the lore the environments. I had some fun playing PvP, but it was never really fleshed out into something great.

WoW was successful because it was popular. Addressing why it was popular is hard... They got people to play the game with good advertising, and the got people to stay in the game with constant gear baiting and updates to add goals for people to stay. The game was also accessible to just about anyone. I think more importantly WoW became mostly a Fad. Everyone was doing it, everyone had friends playing it, so everyone at least tried it. I highly doubt there will be another MMO Fad, as most people who experienced their first MMO through WoW either loved it and stayed and are currently playing an MMO, or they hated it, quit and will most likely never return.

The best thing they can accomplish would be to steal a large subscription base from another MMO. Which is nearly impossible at first release. However, there is an opportunity to new MMOs to cash in big and become the new WoW. Eventually Blizz will release it's new MMO. If it turns out to be a typical MMO release, dismal failures and over hyped expectations, people will either return to WoW or jump ship entirely. FFXIV if it has enough content to draw people in, could capitalize on this.

Anyways a billion reasons why there won't be a new WOW, few reasons to expect another one. But it isn't impossible.