looking back into history i'm wondering why F-35 VTOL didn't follow XV-5A, i.e. placing fans in the wings
http://www.youtube.com/watch?v=1XkJXSoTTb4
50 years ago plane looks more capable as VTOL than F-35. Modern powerful engines allow to drive the fans from the compressor shaft - as F-35 shows - and that would fix the main geometry issue with jet engine placement in XV-5A where fans were driven from jet exhaust.