II strongly support this Request.
Currently it is nearly impossible to build a concave corner in a good design or shape.
There are just a view ways to do that. In the first option the builder is forced to use a diagonal wall segment to connect the rectangular lines of wall segemt's, but with a basement without any use, and a bad look.
The second option is to build a reverse 'stone angular tower' into that gap. But in this scenario the tower roof top is facing the opposite direction.
And this Problem will become more worse, if you want to build a wall consisting of tow blocks width. In this case, the builder have to block his defense walk with a basement.
For concave corner I would suggest a as first solution a 'inverse stone angular tower'.
As second solution a option feature for basements in the building view (for walls), where the builder can activate or deactivate the basement.
And you can use this additional 'option feature' to reduce the list of buildings. For example, you can use this feature to toggle between inner/outer [Tower/Gatehouse] or ordinary/inverse [Wall-Stairway/Angular Tower] or [Towers/Walls] with/without a roof, and so on ...
I suggest these feature for all kinds of stone walls and Towers. And I recommend a proper solution for wooden wall ways around any type of corner and a proper slope solution.
Otherwise all plain designed castles (with out basement faults) will look like a Roman military camp, ... not very medieval
Anyway, you shall also think of round wall corners (concave & convex) and and curved wall segments, too. Have a closer look at this link, 'http://en.wikipedia.org/wiki/Defensive_wall'. As you can see, on early medieval defense buildings. At that time, no one was using a ruler, a plumb-line or a spirit level. They used there eyes and a thumb to get a direction.
If you want to create a medieval atmosphere, you shall keep that in mind.