The only thing that I find unfortunate is that vanilla has already been figured out due to the huge amount of private servers. The real vanilla fans have played it so many times already, they know the best and fastest ways to level, gear up and they'll clear the raids within hours of their release (assuming they are locked at the start).
That's one part of the game I will miss. Other than that I'm sure it'll be great. Hopefully they'll at some point progress the server to TBC and so on.
You won’t miss it if you just treat vanilla like you did back in the day. Don’t download addons to level, take it at your own pace, don’t join a serious competitive guild, and just play the game without trying to min/max. That’s the mentality people need to get rid of. And just play the game