Zhang Jike Footwork Drills
Here's a video (36 sec) showing Zhang doing multiball random footwork drills. You'll either be inspired or depressed.
Now I'm going to let you in on a secret: as long as you are in generally good shape - not too overweight or with leg problems - anyone can be fast as long as they learn one hugely important lesson: It's all about balance. Watch how Zhang is constantly balanced, allowing him to move quickly in either direction. It's when a player leans one way even slightly that he's off-centered, and unable to recover quickly. "Fast" players are fast, but mostly because of their balance. It's not the foot speed that's the limiting factor; it's the recovery time from the previous shot.
Another thing that leads to non-fast play: flat-footedness. Keep your weight on the balls of your feet throughout the rally, knees slightly bent, with a somewhat wide stance. This allows you to dance around the court like a mongoose or a Zhang Jike. (Sometimes the heel of the back foot might touch the ground during the backswing of a forehand loop.)
Another limiting factor in footwork is simply not using it. If you just stand at the table without trying to move, you're not going to develop any foot speed. Even blockers need to dance about the table if they want to be good blockers, as opposed to just reaching for the ball. (Some players reach for the ball and just dead block, usually with dead surfaces like long pips, but they get away with that because they don't have to really stroke the ball. You won't find many high-level players like this.)
So stop reaching and learn to move to every ball. You may never have Zhang Jike speed, but if you think of yourself as being like Zhang Jike and copy some of the techniques that make him so fast, you might not be so far behind. (An expanded version of this might become a Tip of the Week.)