Subclasses are now independent of expansions.To stay “current” with the game, you’d still have to purchase the newest expansion at launch, but this would make catching up much easier with a lot of content continually offered to free players. This year, when Witch Queen launches, Beyond Light would be made free.
In this case, last year when Beyond Light launched, Shadowkeep and Forsaken content would have been free for all players, restoring things like lost free raids and story missions from Red War-era content vaulting.When a new expansion is released, all previous expansions are made free. Destiny 2 changes over to a new “rolling” expansion system.