Love this idea, I've missed out on rare stuff that has come online briefly but has disappeared again before I could nab it. I mean, a man has to sleep sometime!
An option could be "Auto download first 12 results" or "First 12 files" or even "auto download first 12 folders" and "ensure total download size < 1GB" That would keep things reasonable for disk space, bandwidth etc.
For me, I'm usually looking for very specific tracks - and when they are found, there's usually only one result anyways.