It's possible that the thumbs would use joysticks instead of Tetrinsics. 

In the latest TestCut concept, the current thumb Tetrinsics are in the best ergonomic position and yet they still don't comfortably want to move whilst Finger2-4 are in motion, due to mental overhead and feeling like a muscle is about to cramp. With TimerSpy, I don't think a Tetrinsic for the thumb would even fit in the space available. 

Joysticks would be useful for non-typing tasks such as mouse movement or gaming, they're cheaper and takes up less space.

Solution mining... ends, in 18 days.