Peter, this is a hard one for me and I'll be very honest in that I was VERY resistant to breeding and feeding ASF's for the longest time. My husband finally talked me into purchasing a trio last August and I have to admit they have become an invaluable part of our feeding program for the BP's. Especially when dealing with the rescues, the W/C's or the picky feeders - well it's hard to beat the results you get offering ASF's.
What Mike and I are doing at this point is deciding right up front which of our hatchlings are hold backs and which will be available. Those that are marked available get started on rat pinks. When we know who will be that snake's new owner we offer them the choice of what type of prey item they prefer (ASF or regular rat) and what type of feeding style (live or f/t) and then we make sure their snake is on that program before it is shipped out. All of our holdbacks have been started directly on to ASF's.
I would assume that due to the ease of raising ASF's we'll likely see them becoming more and more available as much as mice and regular rats are at the big f/t rodent suppliers.
As far as prey imprinting, we don't see it a lot but we do see it some. A few of our snakes will not take anything but ASF's but that isn't the majority and they might well be like that on any type of rodent offered.