A couple months back we heard word from Blizzard that they would be meeting with the team of Nostalrius to discuss the game. For those not in the loop, Nostalrius was a popular fan-run vanilla server that Blizzard shut down. Both sides sat down, broke bread, and now Nostalrius says Blizzard is interested in bringing "Legacy Servers" to the game!

Eurogamer says these are the bullet points...

• Blizzard wants Nosalrius to help in bringing "Legacy Servers" to life in an official capacity.
• Blizzard has the source code for Vanilla WoW, but it's unknown how many assets remain from the original game. There's a good chance some of these things will need to be recreated which will take development time.
• There's also an additional development time needed to polish off the experience etc...

So looks like things are in the works, but it's a long road ahead. Essentially don't be holding your breath that we're getting a surprise release in a couple days at E3. Good to see progress is being made!