The most trusted private server (nost) had somewhere between 100k-150k active players 1 year after its launch, and showed no sign of slowing before it was lawyer'd into the grave. I'm not sure why people think classic will be some short lived thing. People have been obsessively playing private servers for a decade now, and they only have more reason to play now that there's no risk of their characters being destroyed by server takedowns.Classic but it will taper down to probably 50k hardcore autists over a year and shrink after that when there's no new content to encourage them to log on
The average pleb is going to spend 2-6 months just getting to 60. There will be no shortage of things to ever do, especially if you want alts. This isn't retail.