By the time of the New Jedi Order series Exar Kun was vanquished. He no longer existed. The NJO deals with the Yuuzhan Vong. The NJO is a great series, long, but great.
Exar Kun operation would make no sense whatsoever. There's no way the Jedi or the Sith would leave him there if they knew he was there, and canonicly he's there until the New Jedi Order series (Granted, said series is a complete disaster that doesn't make much sense, but, hey, we have to take the good with the bad in regards to canonocity)
As for planets I would love to see the Zabrak homeworld of Iridonia. No Star Wars game has ever taken us there that I know of.