Your guess is as good as anyone’s. I got #3500 for my pug worth #1000 trade in. i think only #1000 is from the government, some of the rest comes from them selling the parts, e.g. doors, windscreen, wheels, tyres. The engine may well end up abroad being used there!
My punt is that as the vehicles become less ‘valuable’ the deals will decrease. Further there will disappear when the number coming through the schemes are not worth having the admin overhead for.