This tool shows the frequency and number of samples for a sample loop, and allows you to set the loop by specifying the frequency or number of samples. The “Move” option specifies which loop marker to move when setting a loop. Press “p” to show the preferences pane.
(idea from Jonas, here.)
Yes, as well as a “transpose” feature. Right now, the frequency info is only valid for the basenote of the sample, but with a transpose feature you could, say, make the sound loop at 480 Hz when played 7 semitones above the basenote, or, similarly, make it loop at a G#-5 +43 cents (once the note stuff is implemented) when played 3 semitones below the basenote. You get the idea.