i played vanilla. i started in dec the year it was released.not that it matters.
they have said that it was going to be "as close to vanilla as we can get it". meaning it is more of a museum piece than it is not.
they may have some differences on what patch or if they want to fix bugs or some stuff but not something like "balancing" the classes or random qol shit that people keep trying to drill into the game and ruin what could be something awesome.
i may not be blizzard, but i believe in my own opinion that if you want to add something that wasnt in vanilla it is not for you.
that is my opinion though and i dont have the rule of law to enforce it. i only have my words.