I'm pretty tired of generation 1.
Beyond that, I wish Lucario would be replaced by something no one is thinking about or asking for, something that's not pushed as a mascot in any capacity. Something like Scrafty, Cacturne, Ursaring, etc. Something tough and appealing, but still middle-of-the-road in popularity. I feel like that's the primary draw to Pokémon. There's something in there for everybody. Each one is somebody's favorite. That aspect could use its own representation beyond the assists. Maybe even have a second Pokémon Trainer with three odd ones alongside a more predictable one with starters like Red had in Brawl.
Making it into a SSB would rob the pokémon of that status, though, wouldn't it... it's not a perfect idea. But everyone whose favorite pokémon isn't a legendary, a starter, or Pikachu, and has fantasized about it getting into Smash Bros. as a playable character should understand what I'm getting at. Not that my favorite is a nobody... at least, it hasn't been in the metagame for the last three years.