Zooming is used a fair amount nowadays. You see it in the Atom editor, with the shrunken form of the document on the right. It is used extensively in Fancade, which because it is based on a Isometric projection of 3D space, is quite natural. All graphic design products use zooming constantly. The reason you don't see it used that much in programming is that once you zoom text below 6 pt it is illegible, and therefore useless. Seeing the shape of code does not inform you in any way as to the function of the code. Unlike a bitmap which can be sampled to 1/16th of its pixels and still be quite legible, code basically turns to mush when shrunken. Looking at a blobby bunch of wires may be sexy at first glance, but without comprehension it is mere graphical artifice with no substance or actual productive value. I don't find the Atom shrunken text form on the right is much better than a scrollbar.
Zooming does preserve context better than jumping, and i think we will see more of it, but don't pin your hopes on a UI trick going to advance programming significantly.