Here to Help,
You highlight the practical limitations of a low-level CTA base of any description. It's not in the design specs for Class E which the purists espouse. Practically though, even doing a US-style IFR pickup as you describe is fraught with danger. The only reason it would be done would be because ATC couldn't clear you. In a radar environment, that would mean the opposing traffic was pretty close. Throwing caution to the wind and going VFR to get around "clearance not available" would be irresponsible. It would often be impossible for the crew to gather all the info (CTAF on one radio, ATC on the other) they need to come up with a safe plan of action in time.
The only practical option would be to stay on the ground (Dick's beloved E down to 1200/700ft AGL; onya Puece) until cleared. I would be on the threshold, stopping
all movements.
