It's popular to hate exclusivity nowadays, but I've always loved crossover characters when they make sense. Link in SC2 was my favorite example. I didn't feel like it broke the immersion at all. Yoda and Darth Vader made much less sense though. There was a thread recently about Mortal Kombat in Smash and Nintendo in Mortal Kombat, and I thought Ridley for MK would be awesome as a Nintendo rep, as he fits the MK universe's brutal design philosophy better than any other major Nintendo character. Breaking the userbase into two metas each with different exclusive characters is a bit more problematic, but rarely are such exclusive characters top tier, so it's usually not a big deal for the competitive scene. For the casual scene, why care? Just find a friend that has the game on the system with the character you want to try, and buy the game for the system with your favorite exclusive character.