Let’s take a look at where the Hollow World is going.
First of all, if there are disparate cultures loosely based on various real-world cultures, how are they interacting in such a way that a party could include members from all across the Hollow World?
Well, the simple answer is trade routes and crossroads, and the game focusing on one such settlement as a locus of adventure. It means I have to do some work researching trade routes like the Silk Road, and the cultural crossroads those spawned.
Next, how disparate are the cultures?
The whole point was to make an Oriental Adventures-ish setting but done right, with more research on cultural norms and less stereotyping, but also taking influences from Legend of the Five Rings, Feng Shui, Yoon-Suin, Qin: The Warring States, Suwarnabumi, and any other games/settings I can study, and bringing their influence into D&D 5e.
Lastly, is this going to drastically change how the D&D game works? Am I going to have to homebrew a lot?
I hope not. I want to build as little as possible around the core rules, and if I have to I’ll try and visit third-party published materials rather than homebrewing things, just to rely on someone else having playtested stuff already.
I can foresee a problem with a mishmash of everything, but hopefully there won’t be too many disparate threads.
What does this all mean currently?
I have in mind a generic trade hub on the transcontinental trade route where three major cultures (currently) meet – pseudo-China, pseudo-India and pseudo-Arabia.
I need to pull cues from Calimshan/Al-Qadim and Oriental Adventures, go back to other texts and pull better ones, and see what I can put together. It could work great, it could be horrible.
The reason to adventure is to keep the trade safe, to banish monsters, and to achieve godhood in some form or other (I think? It needs some work).
Another setting I want to sit down and playtest at some point. Hopefully I’ll get to soon.