It would be awesome if EA/Bioware made an expansion featuring the return of Darth Nihilus. Here me out on this: I know Nihilus died in KotoR II, but you obtain his mask. Now, the story says that Nihilus ripped his spirit & infused it in his robes & mask. Now, whoever comes across the mask, they would succumb to his power as he possesses their body and return to his eternal feeding.
The story that could be whipped up on that alone would be epic in my opinion.