A trade rumor that has gained a little steam fueled mostly by wishful thinking is the furthest thing from reality according to an Arizona newspaper.
I've read from second-hand sources that Marion doesn't like playing second fiddle in Phoenix, not to mention Phoenix's impending luxury tax predicament, so it would make sense that they're shopping him (again).
I can't imagine the Suns wouldn't listen to an offer involving Wallace. He could provide a more solid defensive option against the top big men in the West and his inside/outside game which would probably flow well with the Suns' offensive game plan. It's clear that Wallace doesn't feel the need to be "the man," so deferring to Nash and Stoudemire at this point in his career would come naturally.
That being said, I maintain it's difficult to imagine a lineup where Tayshaun Prince and Shawn Marion would both start. What would the Pistons do at the center position? Start Nazr, or even worse, Amir Johnson. You'd have the lightest front court in modern NBA history.