My idea is far more crude than yours. I was thinking of nailing (okay, maybe dovetailing) a cube/frame of 2x4s together with a bunch of other scrap wood nailed/glued inside to give it some weight. It would resemble a box like yours, but maybe a bit more cuboid. In my idea, maybe I’d affix some dowels to the bottom which would drop in the dog holes to hold it fast. One large bench screw would be the vise, like a leg vise. And I was also thinking about maybe having a second side (rotate the cube 90 degrees) that would be used as a sharpening station.

Anyway, don’t know if I’ll get to all that but thought it was great to see a fine woodworking type application of my crude idea!