I heard a rumor about other wall types being implemented at at some point.
I would like to suggest that instead of building new wall types, you would be able to upgrade the wall segments you already had built.
Currently people build walls in layers to maximize defense. When implementing other wall types.. people will try rush to best wall available and build that. If you could upgrade your wall segments people would start small and slowly upgrade. Instead of having zero defense or max defense.
The cost of these upgrades should ofc match the strength the wall gains, and perhaps cost less than building a new layer of wall (depending on the strength ofc)
Would be cool if the walls changed texture/height/fancyness when upgraded.