I'd much rather this hypothetical new hub were found somewhere in the Vallaki slums, following a similar theme to the Thieves' Highway found in Port, though perhaps not quite so many areas and so maze-like, unless it turns out that it needs such expansion.
Not caliban/outcast centric, just somewhere they can slip into and coexist, tentatively tolerated, but also isn't just a comic book villain hideout. It could just be some condemned bar, warehouse, antique store, auction house - anything like that, as long as it has a decent amount of open space so people can carpentry up a little extra scenery to make it their own. Player merchants should be allowed to open up shop to offer some level of magnetism to the area, beyond just the RP happening here. Poor and destitute Barovians, forgotten by their own society, squat here alongside adventurers who were injured before their career could take off, and maybe some outcast NPCs in spare rooms or backrooms (just remove all the doors to remind people it's a hub, not an inn), or maybe in the basement which could be connected to the sewers, or up in the attic if you are daring and want to somehow make a "rooftops" area for characters with more dexterity than sense. No rentals here, just a shared space even if there must be a clear division.
It will take some brainstorming, but I think the "bubble" it exists in would be a lot more believable than the circus that is the outskirts. That's the skeleton of the idea. Think of a scaled up Lady's Rest basement but it's actually in the city walls now, so it can be bigger.
Here, it's well in the bounds of setting scope and caliban/outcasts will be judged for what they are, which risks denting the reputation of those who treat with said outcasts. This is a real consequence and an actual RP choice, whereas slipping into the Drain and hanging with outcasts essentially has no downside and you can even get away with not RPing the smell.
If it actually sees some use for a while, this could provide a reason for people to RP in the city more frequently, rather than just pass through it, and from the slums, the rest of the city can be rejuvenated. There's already a bit of activity in the city but by providing opportunities for more RP here, encouraging more RP will have more success. Non-adventuring, religion-skeptical, magic-fearing Barovian natives who are terrified of the caliban will fit in better on their own server if those caliban are actually made to scurry around in the shadows and retreat to the sewers when they become too numerous and too brave. As of now, the two groups essentially do not interact unless some new player gets shot by a guard or some experienced player puts an insane amount of effort in only to end up in a fight or exiled anyway.
This has potential to create friction between characters, rather than distance between players. I do think we need more hubs that appeal to different groups potentially in conflict or competition, without trying to just include everyone or be an adventurer haven. High level adventurers don't need homes, they need causes, and caliban don't need to be accepted, they need a patch of dirt worth standing up for without immediately having to turn to revolutionary tactics. Some areas in and around Vallaki do in fact work for this and caliban have been known to slip into places where they might be able to get some help sometimes. That is a great model to work off of that will support more nuanced characters.
