anotherthing,
You can not give an "Expect Onward Clearance Time" to an aircraft that is not airborne. Once airborne, a hold or delay in giving an joining clearance has to include an expect onward clearane time.
You have given a good basic description of what currently happens but nothing new. Indeed and I must admit that I have never got even close to GWC without being in CAS.
Please refresh what happens when an aircraft which has called has a comms failure before the joining clearance can be issued.
In the absence of an expect onward clearance time watching that high performer set 7600 and start climbing at 4000ft per minute towards FL450 along the flight planned route might leave you wishing you had complied with the requirement to issue an EOC or that the 7600 would only climb at 500ft per minute, 100Kt to 6000ft.
No scrub that - just watching the flight climb into the base of controlled airspace in response to an RA might get your heart pumping a bit faster - especially since the reason why the flight was not climbed by you into CAS is usually because the level above the base is occupied!!
Regards,
DFC