Hi, I've been a total war fan since the first shogun came out and I really love warhammer which I've played for 40hours already in legendary difficuly with the empire and the dwarves.
I might be part of a minority but I like the fact that you cannot simply steamroll and occupy each and every settlement on the map but instead have to find other solutions to deal with the factions you can't conquer...
... BUT I think the way it works now seriously limits the campaigns replayability and is also a bit unclear for beginners.
So here's my thought, why not add a "terrain type" feature to provinces to indicate who can colonize them and who can't?
If you don't want to change anything to the current game balance you could just create two terrain types (something like "grassland" and "barrens" or whatever) and indicate that dwarves and greenskins can only colonize barrens while empire can only colonize grasslands etc etc...
But you could also go further and create more than 2 different terrain types to easily add depth to the game and differences between the factions.
For example here's what I thought: 4 different terrain types: grasslands, forests, deserts, mountains. Each faction can freely colonize 2 of them, can absolutely not colonize one and can colonize the last one but with a penalty (something like an upkeep you have to pay each turn to keep colonies in theses areas).
So things would go like:
-the empire can freely colonize forests and grasslands, MAY colonize deserts with a penalty and can absolutely never colonize mountains
-dwarves colonize deserts and mountains, MAY live in grasslands with penalties but never in forests
-bretonnia can colonize grasslands and forests, MAY live in mountains but never in deserts
-Kislev can colonize forests and mountains, MAY live in grasslands but never in deserts
You could also add variations to subfactions (like one greenskin tribe that lives in mountains, another in forests etc..)
I think this wouldn't take a lot of work to implement and would really benefit the game in making every faction and every campaign feel different.