I'll just put a toe in the water here (newbie to the forum).
Hockney researched Chinese scroll paintings, in which the point of view changes as the scroll is rolled -- the viewer may start out looking along a village street, and after scrolling farther may find himself looking down at the same village street from a hilltop.
Hockney experimented with shifting viewpoint, notably in "A Visit With Christopher and Don, Santa Monica Canyon." (I can't post images yet, but: http://www.rudedo.be/amarant07/wp-co.../Hockney49.jpg
In this painting there is no focus, and so the distinction between subject and background seems to me to be almost irrelevant.
In fact, Hockney describes eliminating points of focus -- human figures draw the eye, so he rendered the two people in the painting as insubstantial outlines. He also felt that right angles become focal points, so he eliminated those wherever he could in the painting as well.
For me, clarity in background-foreground-subject feels comfortable. But also, paintings which blur or eliminate those distinctions (like "A Visit", or some of Miro's work, or Rothko's, or etc!) tickle my curiosity and make me think.