I think Sakurai, HAL, Game Arts, etc may draw some ideas or opinions for movesets, characters, and what people want by looking over sites like this (I definitely bet that Nintendo representatives have been through this thread, and may have even posted here). Maybe to see some of what the fans think, but more importantly, to get inspired. And you know what=??? I think we should all be okay with that. If this was solely a popularity contest, we would ultimately be annoyed by awful choices like Waluigi making it (who is dominating SSBF's poll, sadly for the sake of humanity).
Plus we wouldn't get totally creative and less popular choices like Jigglypuff, Captain Falcon, Ness, the Ice Climbers, *shrugs* Sheik,
Pichu, Marth, Roy, Mr. Game and Watch, Pit, Zero Suit Samus, the Pokémon Trainer, R.O.B., Solid Snake, Captain Olimar, etc. Those type of characters help make smash more marketable, and are a huge reason for the series' success. I think, especially in Brawl, Sakurai has found a great method and way of designing a roster. If the next smash' roster adds on to the satisfying originality and uniqueness of Brawl's, we are in for a heck of a roster.
Now to make the game more offensively explosive....
Hopefully Sakurai, HAL Laboratories, and especially Game Arts watches basketball or football instead of cricket for how the next smash bros' offense should look like...