I'm not sure I agree that Sano should be starting over Plouffe right now. I think that's coming (probably next year), but I do think there's merit to letting 2015 play itself out. If Plouffe is traded, he won't be traded on the cheap. He's a pretty valuable 3B right now.
On the other side, what is the average OPS of a 3B right now? I seem to remember it being in the low .700s. That's the price you pay moving Sano off of 3rd to DH where that average OPS is much higher. Can Sano still be a star in that role? Sure. But if he can play reasonably competent defense, his bat is still far more valuable at 3rd.
Mauer to the OF... I wouldn't be surprised if that's tried this year. I wouldn't mind seeing him get some reps there. If he can cover some ground, that might solve a few of these issues.