I haven't seen this confirmed with certainty, but Alex Kennedy recently twat the following:
That sounds about right. Landry Fields has been struggling and Shump has thrived to the point that he's been finishing games with the first unit instead of Fields. Shump has started before, of course, but that was out of position (we soon learned) at point guard, not off the ball like he'll be alongside Jeremy Lin tonight (should this actually happen). It'll be interesting to see whether he matches up with Tony Parker or Manu Ginobili. Parker's probably too quick and too good a shooter for Lin to guard, but Ginobili makes much more sense size-wise for Shumpert. I also look forward to seeing how Fields does with the second unit. He just hadn't been getting/using the ball in comfortable situations over the last few games, and a change of company might help him regain his rhythm.
Cool stuff. We'll see if this actually comes to pass and, if it does, if it holds up. I suspect it will.