Its way easier to port Freespace to X3 or Freelancer rather than trying to do this.
Its like try to convert Call of duty black ops intro Fallout new vegas.
Maybe it worth a trying to port Freespace to the replacement of X3, that should come next year.
To even try to do this, we need scritps, you know, like the ones in "Runuo Ultima Online server", C++/C# scritps that allow to add objects, variables, effects, a long etc... just take a look at the RUNUO server and you see what i mean.
Basicly half of the engine need to re-done to work with scritps, weapons, ships, etc, need to be converted to C++ objects, engine need to compile scritps at start. a long etc.
Its just a new game.