I’m not enthusiastic about Namco Bandai’s decision to split up Yoda and Darth Vader into separate games. Soulcalibur II had three different guest characters, but they were from different universes. The demand for Heihachi vs. Link isn't as high as Yoda vs. Darth Vader. Star Wars fans will probably pay for the dream match too, if they have a chance to do so.
Sony Computer Entertainment Korea, the distributor of Soulcalibur IV in the region, says it’s possible. This could be a mistake on the product page, but it says you can make a dream come true with Darth Vader vs. Yoda and My Character vs. Apprentice fights through available downloads. Namco Bandai is aware people want to purchase the other Star Wars character so I wouldn’t be surprised to see this happen even if it wasn’t in Namco Bandai’s original plan. Adding to the speculation, but still not solid evidence there is a proposed video of the fight which was pulled from YouTube.
Images courtesy of Namco Bandai.