I've been sad enough to make the exact case in an old, asinine 'Sephiroth vs Darth Vader' thread. There's no force in FF7 and no lifestream in the Star Wars universe, and as the two would work in contradictory ways, there's no hope of a 'battle ground' that would support either mechanic. Sephiroth's Jenova-body held together with manipulated lifestream and tape would fall apart, turning into a foamy mess, and Vader's armour, unsupported by the force, would topple him over. It'd be like watching a fight between a burst fire extinguisher and an anchor.