Oh, for sure it's an issue with the independents ... that's one of the reasons they are going the way of the Dodo bird. MSOs and specialty shops are taking over the world and those guys DO have their shit buttoned up real tight.

Depends on the extent of the use of aluminum. Is it the hood/fenders/bed using Aluminum?
And in 9 times out of 10, those places buy new panels. There is not a whole lot of "repairing" aluminum panels. In my experience most body shops will buy the cleanest panels they can to minimize the work they have to do.

Forward-thinking shops already have at least ONE tech that is aluminum certified otherwise they would not be able to take any Audi or Mercedes repairs. This is neither a surprise to collision repairers nor is it a big deal.