It's kind incredible that Guild Wars 2 has lasted this long.
It turns eight years old this August, and ArenaNet, for the most part, has been a pretty good steward of the game. In all that time it's only hosted two expansions (Heart of Thorns and Path of Fire): otherwise, it's been propelled by its "Living World" seasonal concept that was way ahead of the curve of many others games at the time. Now it's gearing up for another era of the game.
On the official site, the team puts it plainly: "Development is underway on a third Guild Wars 2 expansion." There you have it. Although it's "too soon" to mention any specific details about pretty much anything (even the timeline), they did give us a "piece of early concept art," and the pagodas and cherry blossoms are a dead giveaway that Guild Wars 2 is looking to the east in the future.
Although things are a bit uncertain right now (and ArenaNet is centered in Seattle, where Washington state was hit pretty hard by COVID-19), expansions typically release with a two to three year cadence (2015, 2017). Guild Wars 2 is due for one, but we could be waiting until 2021 for it.
A Glimpse of the Distant Future [Guild Wars 2]