Pierre,
The whole idea of safety is to get rid of as many uncertainties as possible. If the CAA had either put the appropriate airspace in place or prevented such operations then we would not be having the debate about a series of what if's.
Even you say - "B may be unable to issue mandatory instructions outside CAS"
It is that "may be" and all the other may be's in the situation that could reduce the level of safety. Thus the professionals at the sharp end are having concerns.
Regards,
DFC