Honestly I think diversifying the roster is a really good idea. I like Pokemon's selection of characters, because they all feel unique and special in their own way, with each one bringing a new set of moves and play style. (Except Pichu, because he's stupid.)
Fire Emblem is a series that is HORRIBLY represented, considering there's so many different classes and weapons in the game, yet we have 5 lords, a mage, and a manakete. And all of them use swords. What ever happened to axes and lances? There's also bows and other weapons to choose. Half of the series is represented with echoes and semiclones which doesn't help either. 6/7 of them have counter as a down special. 4/7 have dancing blade as a side special. Representation wise, the best choices would be Marth, Ike, Robin and Corrin to keep the FE roster more diverse, while adding new FE characters that would bring something brand new to the table. Either that, or you could declone some of the echo and semiclone characters to keep them more unique.
Zelda is another example of bad representation. We have 3 Links, 2 Zeldas, and our main villain is a Captain Falcon clone. I'll cut Sheik a break since she's actually unique. Ganondorf was added last second due to time constraints in Melee, but he's had 3 more games to get decloned and have a unique moveset. Instead, he's been getting slight adjustments every game to make him slightly less similar than Captain Falcon. Also, 3 Links? I get that everyone is here, but this is ridiculous. What's next, CDI Link? They all play very similarly, with mostly slight differences. Regular Link is the most unique with the remote bomb, but Young and Toon Link have many items and abilities to use from their respective games. It's a missed opportunity. Why can't Young Link use the many masks he finds throughout the game to use different abilities? I'd be cool with cutting one, and decloning the other Link, while adding some new Zelda characters that would bring a new set of moves, such as Skull Kid, Midna, or Ghirahim.
I hope Sakurai takes these things into consideration when developing Smash 6, but the dude needs a serious break, and this game is amazing as is. But I still like a lot of these characters, even if they are missing a lot of potential.
Also, I'd love for more fan favorite requests to finally be able to make it in.