Presumably, somewhere in Renoise 2.8 is code that jumps to various positions within both the sample (0Sxx) and sample envelope (0Exx).
I think it would be a nice idea to have a sample meta device that receives a meta value (from an XY pad, velocity tracker, note tracker, lfo etc.) and affects either the sample offset and/or sample envelope offset as an instrument command would.
This could make some funky effects e.g. playback position to velocity, modulation of pitch/panning (via instrument envelopes) etc.
Just another idea for a future version.