Diablo 4 will have 'an army of developers' working on years of seasonal updates

pcgamer.com:

Diablo 4 will be supported by an «army of developers» working on new seasonal content for years to come, Blizzard said in today's new quarterly update(opens in new tab), with updates and new content ranging from polish and quality-of-life features to major new features, quests, enemies, items, live events, and—of course—season passes.

Seasons in Diablo 4 will be modeled after Diablo 3's: Players will begin each new season with a brand new character (existing characters will remain accessible in the «Eternal Realm»), with no items or gold from the previous season carrying over. 

«We think it is important that players see that the game is changing in meaningful ways,» associate game director Joe Piepiora wrote. «Each season will be released with a fresh new gameplay feature and questline that introduces new challenges, mysteries, and possibilities into the level-up experience.»

Seasonal live events could include things like a weekend-long invasion of the Drowned (with advance warning, so players will be ready for it) or the arrival of a new, presumably passing, merchant. Season Journeys from Diablo 3 will also return, offering time-limited rewards for players who can complete certain tasks. Season Journeys are separate from the season pass and free for all players, but completing Journey objectives will grant progress along the season pass.

Season passes will offer cosmetic items and premium currency along both free and paid reward tracks. Boosters that accelerate progress through the season will also be up for grabs in the pass, but because they impact gameplay they will only be on the free track—and while players can purchase season pass tiers directly, doing so will not speed up access to season boosts because they're