This is a place where your wrists can rest while you type. I printed with settings to leave the infill exposed, which makes it a little flexible.
This is sized for a pok3r my pok3r keyboard. I think it would scale well, but 50% of a full sized keyboard might still not make it on most printers.
I had to make two pieces (left and right), because the whole thing was 290mm.
If I was going to make this again, I would make it more flexible, either by reducing the thickness of the shell (and remaking the stl from the .py) or just by reducing the % infill. A little roundover on the front might be nice too, but I'm not sure how that would work with the infill pattern. You could also remove some of the material (in the CAD files) underneath the front and back edges so they flexed a little, but I think that would move my hands enough to bother me.
I sliced with Slic3r, and set the number of top and bottom layers to 0, and set the infill pattern to rectiliner, which makes this neat pattern, and leaves the structure a bit flexible.