I have an idea for creating a spherical world that does not depend on latitude and longitude.
First, we start off with a sphere that has a planetary radius.
Next pick two points on the sphere, make them relatively close. The first point will be the origin of your map. The second point gives you the direction for the primary axis on your map. Using the normal of the first point and the direction to the second point, you can find the secondary axis of your map using a cross product. You now have a gnomon, an anchor for your map.
You build your map as you normally would then transform your map to the gnomon.
Later when you want to add to the world you reverse the operation lifting everything inside the reference grid and transforming it to your flat work area.
The slight difference in vertical as you move around should not be noticeable.
I am not sure how you would implement this in game, but I think nine partitions would be sufficient to hold enough of the world to make it believable.
Please remember that this is just an idea from somebody who hasn’t created his first game yet.