I like the concept, but if we create a layer for different points in time, it'd be a terrible mess if e.g. terrain is updated on Universalis, meaning we'd have to change all the layers.
Actually it may be possible, if we just don't edit those areas that aren't final yet. For example I could make old borders for Blaist Blaland-region without drawing on other areas on the map that aren't final, and then they could be edited when they are actually final, and there could be just a base map layer that'd be the only one needing to be updated if we change terrain. That should work.