Thanks to a section in the newest Weekly Shonen Jump, translated by Gematsu, we now know a little more about how Dragon Quest Builders 2 fits into the canon of other Dragon Quest games, and it's following a similar template to the first Builders game.
Where the first Dragon Quest Builders was a sequel to one ending of the first Dragon Quest, where the player character chose to take power offered by the villain rather than saving the world, Dragon Quest Builders 2 is similarly a sequel to the events of Dragon Quest 2.
In Dragon Quest 2, a corrupted cleric called Hargon planned to sacrifice his life to summon Malroth, the god of destruction, to destroy the world. The plan ultimately failed, but apparently a religious order took over Hargon's plan, and carried on his legacy.
After this religious order arises to destroy the world, and destroy all those who know how to rebuild and repair what has been destroyed, Dragon Quest builders 2 starts with a protagonist who has been arrested for being a builder, because someone who can rebuild the world poses a threat to an order wanting to destroy everything.
The story also contains a young boy called Malroth, sharing his name with the god of destruction, the mystery behind which is likely to be a core part of the plot.
Dragon Quest Builders 2 is coming to Switch and PS4 some time this year.