The flex issue was in my mind as well. Another thing is that I'm not sure how far off center you can place the FC and get away with it. If you lay this out on paper the lengths of wire involved are disturbing which is the main reason this has not yet come to fruition. I then worried that I might be making some sort of electro-magnet.
Many FC's do not mind at all being off-centre - I know for a fact that OPenPilot (CC3D or Revo) doesn't mind at all: you can place it anywhere on the frame.