People will get bored with Vanilla quickly.Its all fun and whatnot on private server,but retail is whole different story.On private server,you can log in once a week,on retail you gotta actually play,because i strongly doubt someone is willing to toss money away,even that small sub, amount of money.
People forgot what vanilla wow actually was,and how boring and painful it was.You couldn't even play half of the classes,you could but...All that farming,in Vanilla,you can't farm previous expansion to earn gold,you gonna fight other 3-4 k people especially today (well in 2019) generally speaking,where everyone is trying to earn money by selling gold.Good luck having fun getting oneshot by rogue streamers,who lived past 14 years for Vanilla release only.
And again,have fun playing shaman,paladin,druid vs 90% population who gonna play swifties,vurtnes,drakedogs and rogues.