I think what you're mentioning is something that worries some of us. How far will Sony dig for these characters? Will they just play it safe by picking characters that a lot of gamers will instantly recognize? Even a character like Fat Princess is kind of a safe pick if they're going in that direction. It's a popular current gen title.
Part of what makes the Smash lineups so good is that Nintendo is willing to dig into obscure or just really old titles/products. We've seen them include R.O.B., Mr. Game & Watch, Nana and Popo (Ice Climbers) etc. But will Sony do the same? Will they dig into the PSone catalog to pull out characters like Tomba, Robbit (Jumping Flash) or something completely off the wall like Little Devil (Devil Dice)? Will they find a way to include the Pocketstation (which would probably be more like an item in the game)? My worry is that they won't.