I played Divinity II many years ago, and the two most remarkable things that I remember most fondly of the game were the Tower the dragon-knight uses as a base and the Patriarch.
I played every divinity game since, and none of them gave me the same feeling as the tower, I think the Hall of Echoes is an opportunity to make it right!

To be more specific, here's what I liked from the tower of Divinity II and would like to see again:

- It isn't shoehorned into the game, you hear and know about it (hell, you can even be briefly teleported into it way before you know what's going on), you work and you fight for it. This gives a sense of satisfaction, having worked to get this amazing reward, making you enjoy it way more every time you make use of its resources.

- It has choices and consequences, you had to choose and work for each NPC that would help you in the tower, and when you got their trust, they became loyal and helped you however they could.

- Well voice-acted characters with distinct and great personalities. Every servant you had was fun to interact with, this made the tower feel much more "intimate" and valuable to the player.

- Convenience. In the tower you could do pretty much everything you needed for your adventures, it was truly a useful base to prepare for new challenges.
I understand this could take away a little from the rest of the world of D:OS II, but think about it: you meet the world greatest alchemist hidden in a small house inside a huge forest, how cool would it be to convince him to move to your place, where he would have new toys to play with!
This would also work in the sense that it would take a while to make the Hall of Echoes the ultimate headquarters, you would slowly be rewarded throughout the game with the convenience of having certain services and bonuses available in there.

- Meaningful upgrades. My memory is foggy in this specific matter, but I think you could do something extra to get special things from your servants, adding depth to them and making you enjoy the tower, its characters and its rewards even more.

You could adapt these things to the D:OS II universe in a seamless way, an example would be: since the game has a lot of crafting your character can do, the NPCs would not just sell you the stuff, they could work like crafting stations, where you do the crafting and get various bonuses since they are there to help you. Of course, for non-crafters they could sell up to the second or third highest tier of items, for a significant price.

I'm sure there's a lot more I could say about this, but I would have to play the game again to remember everything. The point is, I want the devs to be inspired by this fan favorite content they did in the past, doing it even better with all the resources they have nowadays!

I would love to see what you guys think about it, I'm sure more people enjoyed that tower like I did!