Every Nintendo character has canonically talked. Mario says stuff all of the time (but if you need proof, see the ending of Super Mario Galaxy), Link said "I found an item" in Zelda II and "Come on!" in Wind Waker, Samus narrated the intro of Super Metroid and was quite chatty in Metroid Fusion, DK spoke at the end of DKC2 (or was it 3?), Kirby explains his copy abilities in the Pause screen... even Mr. Game & Watch had a few words to say in Game and Watch Gallery 3 (or 4?). Of course, then there's the non-canon things like the Super Mario Bros. cartoon, the Zelda CD-i trilogy, etc etc.
Thus, making the characters talk, while going against the spirit of Nintendo's silent protagonists, it wouldn't be unprecedented. I would still prefer Link to be silent, which could have some gags associated with it (everyone knows what he means without him actually saying anything), and Kirby would be much cuter if he was based on the Kirby anime (only saying "Poyo" and variations, but that might make him seem like a Pokemon).
As for the feasibility, I think that a Smash Bros. adaptation would work best as a Japanese manga or American comic book. I'm not sure why, but it seems that there would be less licensing issues, as there's no music or voice actors.