Classic will take a steep nose-dive. I'm already done.
Streamers will inevitably move to other games as their audiences get bored of the same stuff and start complaining.
The current videogame market is better than ever, so there's always stuff to play. People are not playing Classic because there's nothing else, they are playing it for a quick fix of nostalgia.
Destiny 2 Shadowkeep is out soon. Blizzard will announce new stuff in BlizzCon, the Classic hype will die. As it should. It's a shitty, old game.