I've yet to actually play a Professor Layton game, but I'm playing the Layton Brothers: Mystery Room for ios per a friend's suggestion. From what I've read about the Professor Layton series, it seems Mystery Room doesn't really play the same. Mystery Room seems more like Ace Attorney, but nevertheless I'm enjoying the game quite a bit - it's very well written, especially for an ios game. I'll probably get into to the actual Layton games when I'm done with this one.
Despite not actually playing a Prof. Layton game starring Prof. Layton (The ios version stars his brother, Alfendi) I still think he would make a great edition to the cast, albeit an unlikely one. Sakurai, however, seems to like to create characters that no one would really exect to be in Smash - giving them unique and intelligent movesets. And Prof. Layton certainly fits that bill, puzzle solving would be a very interesting mechanic.