That was one of the hard question we got. I say hard because we are so "early" in the design of the game for some mechanics that it's hard to answer without giving spoilers or false hope.

I was in some kind of rush earlier to answer the question because it passed under the radar and we had a lot of other questions to answer so I gave it a go. Now that I have more time, I'll answer it as Jeff the gamer. That means that everything that I say after this is what I would want to have not what we will put in the game

Also, I haven't read all the topic in detail. That's a LOT of stuff to read. I'll still need to read all of it at some point though.
Anyway.

If I take Path of Exile Hideout for example. This is the kind of stuff that I like. Does it fit for DOS? I don't think but....
- You can bring two NPC to your hideout.
-- They give you daily quest
--- This encourage you to come back every day to do a random generated quest related to the NPC
-- They give you a crafting bench that is really helpful
--- The crafting bench is better the more you level your NPC
- You can customize your Hideout with A LOT of assets
-- Path of Exile staff are doing "Hideout of the Week" community highlight so it encourage people to tweak their hideout.

The thing I like here is that a lot of the stuff is linked to some mechanics in the game.
The NPC that you bring are NPC that you help in the game. The daily quests they give you help leveling them, give you loot and experience also. The higher the level the more crafting stuff you can do. The crafting is related to their economic system. The asset that you can put in your hideout are bought by reputation that you get from the NPC themselves by leveling them.
Their hideout is simple enough but linked to some of their mechanics.

For me, I would like to have a hideout linked to mechanics of DOS. Something that encourage you to go back there and help you in the game.
Daily quest? Probably not, "grinding" is not a mechanic we want in DOS.
Customization? Probably, it could be great for some people I guess. It should be linked to something though, or create a money sink maybe. But since the loot are a finite thing is DOS, maybe that's not the greatest idea. (I'm brainstorming like here) If we add random event in the game it could work, I don't know.
NPC in the stronghold? For sure, lots of quest potential.
Maybe we could have an Arena, that you can customize to your liking. You could put traps even maybe and then invite your friend to juke out in it. But it's not THAT great for single player. And so on...

All in all, like I said, what I would really like as a player would be to have mechanics that encourage me to go back that are also link to other core mechanics of the game.
Everything needs to be linked in my opinion.

(That's a longer answer)