I find that I often would like to play grains reverse. Especially the grains from percussive sounds are still quite recognizable. I helped myself using reversed samples, but a cahnging the play direction of the grains in real time would be much cooler.
Perhaps with the direction beeing modulatable:
* modsource-value >= 0 is play forward
* modsource-value < 0 is play backward
For CV the threshold might be 2.5 Volt