And what has gotten my curiosity is that I haven't found a single shot by Fed this year (with the new pj), that he hit with the white side on top. I'll be fine if it turns out it is nothing, but as I tried it myself, I was quite surprised by the result.
I guess there are two parts to all this:
What's the reason for Federer having the racquet always in one orientation? This has now been put to rest by RJYU - Federer has his grips/overgrips done the exact same way on each racquet so it's the wrapping/bump that determines how he holds the frame - and not any weight.
Does putting in some weight at only 3 or 9 positions help in any way? This is actually a very interesting idea. I also wonder if it would be a little 'mental hint' to drop the racquet head before contact to generate more topspin. I know I sometimes hit too straight through the ball, don't drop the head enough to brush up on the ball ... i wonder if putting some weight on the 'bottom' side would help in that - would you actually feel the weight and remember to drop the head down? Anyways - interesting discussion irregardless of it not being something Federer does.