I tend to agree with your description in the FS section... I see how the speedo sensor on the rear works for speed, and the mount on the DT looks like it could easily hold a cadence sencor, seems to be about right for having the crank-arm magnet flash by. I think a CO2 bottle would be in the way down there.

Of course, these days, not a lot of wireless cyclos would be able to xmit from the back wheel, but the cadence sensor would still work, if you could get it to mount on that peg. It also would make a nice light mount if you could find a small enough LED light.