Calling it now - Legion Classic will be so popular that Blizzard will be forced to keep evergreen servers of the xpac running indefinitely. The infinite grind is what all WoW players crave.

>Retail players are bored to death of the weekly timegates on power progression. They desperately want something they can grind 24/7 to make their character stronger.
>Classic players want a classic+ so badly that they are going bonkers over a private server that doesn't even function. They are even flocking to OSRS for a game they can keep grinding at.