I just thought I'd add my idea for Rotary Encoders and Potentiometer shields.
Hopefully you will like the idea Ken, I'll get one for free.
As you mentioned, it may only be feasible to make one with only encodeing chips. I can see that and that would be fine for me.
For those who wish to do no soldering, it might be good to be able to just clip in on top.
My first idea is a handgrip, with encoder as a remote follow focus control .. probably wireless.
This is for when I have to mount a camera on a crane or jib arm, or up on a pole.