Having been used to CDJs, I don't see an easy way to do this on an RX. For a CDJ, you have to bite the bullet and load up the track.
This would be handy, but I'm curious how you would go about adding it to the cue mix... would it duck the existing headphone feed and feed the current selection? How do you handle track gain? Where would you start playing the sample? (I wouldn't want it to start from the beginning, maybe pick some configurable cue point, etc.)
Big thing I see is that poor USB2.0 interface having to slurp out gobs of data to render the samples as I'm scrolling and scrolling...