I just finished the prototypes for a design I've struggled with for the few years or so.
The original concept was a set of fully modular boards for use with wargaming, but there is opportunity to use it for roleplaying scenarios as well as diorama layout (or just shelf displays of models not in use). Each board will be textured, and the entire set is designed to interlock into whatever layout you would like. I will be releasing various 'terrain' sets as each terrain type will demand different texturing methods and detail. Note that as this is a prototype, I've not touched up the seams as of yet.
The design is such that it will support fairly deep depressions as well as heights, and will have larger modular-hill and valley sections, all made from cardstock. I've shown this here with some 40K models for scale. Each board is 30cm x 30cm.
Enjoy!
Sean