"isn't that exactly what the European 20M class is for?"

BIll, as that's a racing class which to me is an even more demanding set of instruction, that wouldn't be a feasible instruction means for volume processing of co-pilots. I think you may mean that such a class would foster more dual XC soaring in general. That I'd agree with esp. given the aging pilot population (older pilots flying with a safety pilot), and more people enjoying two seat flying, I know I do..... so long as they don't smell bad....

It still comes down to bringing together at least 4 variables at once: two pilots, weather and ship availability. The tightest constraint I see is the PIC who would do the mentoring, paid or not. How to incent more of them to provide time in this role?