Blizzard finally offered a response after shutting down the private server, Nostalrius. They explained their reasons as to why they to shut it down and what sort of steps and talks they're taking next in addressing the community's desire for a vanilla World of Warcraft experience.
Game Informer summed up a lengthy post on the WoW forums by executive producer J. Allen Brack, who explained...
Why not just let Nostalrius continue the way it was? The honest answer is, failure to protect against intellectual property infringement would damage Blizzard’s rights. This applies to anything that uses WoW’s IP, including unofficial servers. And while we’ve looked into the possibility – there is not a clear legal path to protect Blizzard’s IP and grant an operating license to a pirate server.
Brack goes on to explain that Blizzard has looked into opening “Pristine” servers where they remove character boosts, recruit-a-friend bonuses, World of Warcraft tokens, and access to cross realm zones. But most people in the forum thread noted that they did not want a “Pristine Realm” but a vanilla version of World of Warcraft. In fact, further into the thread most note that a “Pristine Realm” completely side-steps what people were asking for.
So what were people asking for? Well, they were asking for a vanilla server of World of Warcraft without all the changes and alterations that came with the expansion packs. There was a Change.org petition that managed to gain more than 238,000 signatures for Blizzard to allow players to access a vanilla server for the game. In fact, that's what made Nostalrius so popular for the year it was in operation.
According to Brack, that's just not technically possible, stating...
We explored options for developing classic servers and none could be executed without great difficulty. If we could push a button and all of this would be created, we would. However, there are tremendous operational challenges to integrating classic servers, not to mention the ongoing support of multiple live versions for every aspect of WoW.
The next logical question that went unanswered by Blizzard, was “why couldn't they utilize the same setup as Nostalrius for the official version of World of Warcraft?”
Some argued that the cost of setting up a vanilla server wouldn't be worth it given that there wouldn't be enough people to justify that kind of investment. However, Nostalrius had 800,000 registered players. I don't see how 800,000 players is a negligible number. That's not to mention that 150,000 of those players were basically online regularly throughout the operation of the server. That's like combining the average number of daily active users (from the Steam stats) in Team Fortress 2, Garry's Mod and ARK: Survival Evolved together.
Of course, the more technical questions regarding why the vanilla server wouldn't be possible weren't addressed. However, Brack did mention that Blizzard has been in touch with the volunteers who ran the Nostalrius servers and he states that they plan on having more conversations with them. So not all hope is lost when it comes to possibly seeing a vanilla server for World of Warcraft sometime in the future.