That is a good point, I believe it should be fine, but you are right about spring, the TB whatever is being used as the slave TB must have a spring of its own as well, I think the motor is plenty strong, if it lasted well for most people who did the crazy mod by forcing the 45 degree of there Throttle Position Sensor (TPS), which pretty much made the motor fight against the users foot all the time.Nice update with the pics.. looking at the concept more, I was curious do you think the stock motor assembly will have enough torque to pull another throttle plate with its own spring? I mean, the place where you have the cam attached is where the throttle plate used to sit, and it does not have an additional spring there stock. So to pull on another cable throttle with its own spring might put extra strain on the motor / clutch?
Also I have messed with the whole system and springs are pretty strong even in normal working conditions, so under normal conditions the motor has to move the butterfly constantly with all those spring forces acting continuously.
This point also brings me to the search of throttle cables, I guess it would be very important to minimize any restriction or resistance so that the whole OEM system can operate properly.
The biggest issue will come to ITB setups, were proper spring loading will come into play