Did you finalise the list of houses that you want to put into the game?
I wanted to try making a Westeros map for a while, partially for my own reasons, but it would be useful for the mod too.
If I knew how many houses will be in game, it would help me to judge the scale. The map would have to be around 3-4 times larger than bannerlord's map if you wanted to make a castle/city for each house like in the game of thrones CK2 mod, so it would have to be cut significantly. The main problem that the North is sparely populated, so it would work well enough, but then you get to the south and there would be castles/holdings on top of each other. I also noticed there's a huge lack of cities in Westeros there's King's landing, White Harbour, Gulltown, Oldtown, Lannisport and MAYBE Hardhome, that's about it, and obviously you could make every capital (Winterfell, Sunspear, etc.) But you would still only have approx. 12 canon cities vs Calradia's 50 or so, So a decision would have to be made about which houses get upgraded to cities, and which ones will only gain castles.
For gameplay purposes it would be best to keep the map very evenly populated just like in bannerlord.
Obiously it can't be modded into the game until mod tools are released, but it would be great to have something ready for when the time comes.
Also, any reason you aren't joining the other game of thrones mod team? Don't take it the wrong way, but the idea of alternate history of event's don't justify a whole new project, you would all accomplish more together and faster. The alternate history bit could easily be an option, or a sub-mod for a bigger project.
I'm going to be putting as many houses as I can reasonably get ingame, and will be taking gameplay over canon in regards to cities. "Mount & Blade Cities" are basically just large castles with the amenities, so I don't think its too far of a stretch to use them for larger castles. GRRM is also notoriously bad about sense of scale in regards to supporting populations and the like, so filling in gaps is going to be necessary no matter what. I want an even population of civilization where I can, so likely there will be a ton of towns/villages/castles added just to make sure there's not an extensive amount of dead space.
There are like ten teams making ASOIAF themed mods. Some of them are focusing on the show, some on the books, which are major divergences already. Most are focused entirely on sticking strictly to the canon to the letter and the story events beat by beat. I don't want to do that. I want to create a world where people can roleplay any house they want, drop in and be a Tallheart Swiftfoot running around the woods of the north, a Belmore in the Vale fighting the Mountain Clans. I really want to push the idea that the houses are the true characters of the series.
And more branches the better, combining teams and ideas doesn't make a better product in the end and certainly combining teams doesn't get things done faster. Everyone has their own visions and ideas, and we're all basically making different "games" entirely. I'm focused on high fantasy, obscene armor designs akin to the miniatures game whereas others are going hard realism only. I'm working on heavy troop trees with tons of unit variety, others want them more streamlined and efficient.
I respect all the other mod authors, but they're doing their own projects, and mine is much different than what they're putting out and we have seen. The alternate timeline also completely avoids spoilers of the books/show which as someone who got the books spoiled hard by ACOK by accident in Warband, I didn't want that to happen to someone else. It also means I'm not beholden to what happens in TWOW/ADOS when they drop as well.