To expect all IFR/IMC flights to use CAS is completely unrealistic and such a suggestion presumably comes from non instrument rated pilots.
IFR helicopters are routinely required to operate in IMC in transit of Class G. Most helicopter flights begin and terminate outside controlled airspace and often there is no CAS to utilise. I try to transit CAS where able, as I see a control service as an additional help to maintaining separation from other traffic. However, it doesn't always guarantee separation from gliders who can and will operate inside CAS without talking to the controlling ATC unit.