A recent Kickstarter update says this about the new area:
This new and mysterious realm is a world of mystery. This ominous place has a connection to both the Void and the realm of the Gods.
According to Larian Studios:
Who knows what kind of adventures such a realm will bring to the main game.
Adding the Hall of Echoes was the last original goal that Larian had for its Kickstarter. However, with the great success of raising over $1.5 million, Larian added a variety of more goals for their Kickstarter - all the way up to $2 million.
Their next goal is to hit $1.65 million and create a team devoted to mod support.
Divinity: Original Sin 2’s Kickstarter has achieved a lot with its 33,000 backers, and there are still 11 days remaining for it. However, Larian has offered another option for those who are unwilling to make use of Kickstarter. If you want to help Larian’s quest for funding toward Divinity Original Sin 2, you can also help through the use of PayPal.
