Beags,
Seems eminently sensible, but I anticipate that ATCOs will want mode C in classes E-G where it underlies classes A-C (which is basically everywhere), to avoid having to call traffic (and spurious TCAS activations) on low-level VFR. Of course, one solution would be to mandate mode C for IFR and prohibit mode A only squawks for VFR - mode C or nothing...
Tim