I don't get the nostalgia of the Vanilla fans. In fact, every time I wanted to re-play any game I liked some time ago, I get bored very fast, and often even disappointed. While I don't like everything what happens with retail WoW, I rather don't want them to move backwards like with the no-flying abomination which is so en vogue with devs currently without any reason, or cutting down on content you can accomplish with queueable dungeons. I don't want a game where most of the specs are badly balanced and not playable in relevant content, I don't want a game where most of the cool zones, mounts, pets, and equipment is missing, I don't want a game which is full of grind (I would also like to reduce grind in retail WoW, but Vanilla was surely worse. Just think of fishing...). I also would like to keep my BE, Goblin, Draenei characters, as well as my Horde Paladins, Alliance Shamans, DKs, Monk and DH characters. I also enjoy pet battling from time to time, and have more fun soloing legacy raids than running them on the "appropriate" level. Been there, done that, want to add a new experience in my game, not living in the "Groundhog Day" forever.
And I bet if they should ever install Vanilla servers, then this will costs us more than a raid tier.