People have been working on this idea since probably FS2000, and still no one has figured it out.  It would take a complete rewiring of the contol systems of FS.  Too much to do to have it be an addon.  FS would be completely changed, so you wouldn't be able to use ANY addon aircraft that currently exist.

Trust me, when it does happen, you'll know!

in the simplest of terms, whats needed is the ability to set the engine thrust at an angle other than straight back, (eg X35's lift fan) and vary it in flight (harrier, x-35 main nozzle)... simple....    i wonder what kind of alterations this would need to the FS physics modeling?

interesting point about this kind of alteration not being back compatible.. i agree there, but perhaps once it was built into the physics modeling, it would only require somthing like an extra figure in the cfg, or a set of figures, just like flap angles, so addaptations could be made to current aircraft;s cfg files... just a thought.