VarAC already handles rig control via CAT, and does it well.
What it doesn't do, at least for the radios I have, is update the frequency shown when it's changed from the radio.
In other words, you have the frequency list at the top right corner. Selecting a frequency from the list changes the frequency on the radio, but changing the frequency on the radio does not change the frequency shown in VarAC.
An example where this might be of help:
If I use the VarAC list to select 14.105.00 and accidentally nudge the tuning dial on the radio to 14.105.35, I won't know why I can't connect. If VarAC displayed the radio's VFO frequency, as read by using a CAT command, I might see what the problem is. The rig's VFO frequency displayed in VarAC would serve as a way of confirming that everything is working properly.
Another idea, if the first is implemented: If the frequency shown in the VarAC frequency list does not match the radio's current frequency, the radio frequency display could turn red to indicate a mismatch between the radio's actual VFO frequency and the frequency selected in VarAC.