If made carefully, I don't believe the turning would be heavy.
Just to let you know, I don't care much for the "modular" idea either. Personally, with your design, I think the entire mechanism sitting below the CP would be obtrusive. Also, while sitting at the cabinet, the steering wheel may be in the way- (Although I'm 6'7").
I'm sure that your drawing wasn't to scale, but you may want to check the overhang of your control panel to see if the entire steering wheel and extension arm will actually fit below the CP.
An alternative to my design, would be to put the encoder with the steering wheel, but then you would have an to disconnect the wheel and the circuit for the encoder.
JD