This keyboard has no support at the base of the palm. It isn't needed! The keyboard bears directly on the thumb. The main difference between this keyboard, and the others is that the thumb position is lowered. The thumb is now positioned between the index and middle fingers. Most of the bulk of this keyboard is now structural. The kingpin only extends beyond the width of the palm because it's made of cardboard. If it were made of something stronger, it would only need to go 1/4" beyond the palm.
I'm becoming more satisfied with the thumb configuration. I think it needs to be even thinner, but I'll have to make it out of something stronger than cardboard. I'll try wood, I think. It will take hot-melt glue well and is strong enough.
UPDATE: Since I know there will be a Mark VI keyboard, I tried cutting off the kingpin beyond the width of the palm. Seems perfectly sturdy to me.