I agree with some of your post but I don't believe there is any love lost between the movers and shakers in the BGA and the VGSs. To help with the instructor problem the BGA could come up with a bridging scheme between a A1/A2 Cat VGS instructor to become a 1/2 or Ass Cat BGA instructor, that should be relatively easy and just involve effectively 'differences training' and an assessment. I agree that for Full Cat BGA then the whole training process as for any BGA Ass Cat should be followed.
If there was a will there would be a way. For the BGA this would be an incredible injection of youth into the organisation (that tends to be a bunch of blokes at most BGA clubs I've been to) and for the Air Cadet gliding it would dig them out of a huge hole and free them from the ridiculous over-engineering and regulatory shackles of MAA land.
What sort of bridging scheme could you envision? They would have to attain the same standard as a BGA instructor, why have two schemes to get the same thing? The biggest issue might be that to become a BGA instructor has required an FAI Silver 'C' for quite a few years.
It might also be necessary to get away from a 'gliding course'. However the experience at my club was the biggest impediment to ATC cadets having air experience flying at my club was the ATC. We were approached, we had an initial meeting, told them we couldn't do anything that summer as the calendar was full, said for them to talk to us the following winter when the flying calendar was being arranged, so they came back in the Spring which was too late. Then they asked that for air-ex all instructors be full-cats, where BGA air-ex flying is mostly done by BIs.
I'm still not clear if the current (or maybe I should say future) purpose of ATC gliding is air-ex, which could be as little as a single 20-minute flight, or some meaningful instruction.
Could the BGA cope with an additional 41,000 cadets ?
Probably not, but right now what flying is the ATC providing them with? How many hours a year (on average) did the ATC gliders fly?