Doc,
Having any kind of RF transmission is currently forbidden under the U/C rules, so the spread spectrum part of the 2.4 GHz radios must be non-functional, i.e., no RF sections allowed in the "transmitter".
What Chuck Snyder and others have done, and what Clancy's controllers do, is to put the variable width pulse that is used for RC servo controls onto the control lines, without the radio frequency (RF) carrier. Chuck uses the feature that some radios have of a direct servo link output. A number of JR and Futaba radios have that feature, called DSC for Direct Servo Control.
You could do what you propose very nicely, I agree, by adding the 2.4 GHz radio system to a U/C airplane. Having the spread spectrum features does away with some of the frequency interference problems of the older FM radios, and you wouldn't need the insulated flying lines.
The FCC has allocated some FM channels for surface use only, I don't know what allocations, if any, may have been made for the 2.4 GHz band. It is always wise to tread carefully in preventing interference with other radio services. Perhaps some of the SH bunch with more expertise can comment on this as I don't have any idea about how many "channels" the spread spectrum radios may have. I have heard of some interference issues with these radios.
John W