I think that's nearly impossible. It's a great idea, don't get me wrong, but I don't know how much content can still be added to the second disc. Creating new dungeons from scratch, adding new textures for Gears, enemies and scenario, creating new 3D models, creating more lines of dialogue... That would take a lot of space in the CD, wouldn't it? Maybe the game would need a third disc. Unlike FF7, Xenogears almost has no dummied content to remove.
Yeah, I know... But it's maybe not as much of a long shot as, say, a remake/remaster