-Diverse moveset possibilities: proven capability in fencing, inventions such as the Slot Machine Gun, St. Mystere Glider and the Catapult, and in-game nuances from the hundreds of puzzles could build a moveset simply. These diversities offer a lot of "mind-game" potential which would make him a very interesting character.
-15 million game sales across seven games. Well above StarFox and just shy of Metroid, so relevancy with respect to sales is not an issue.
-High popularity on tumblr and Twitter, strong female support, (a demographic Nintendo want to expand within Smash) and placed highly on many gaming news websites' "characters that should be in Smash" lists. Was rumoured to be a character included in Brawl, and rumours of his inclusion have been circulating since. These rumours need to be put to bed with his inclusion.
-The Layton franchise debuted on the DS, and we have yet to receive a character from a franchise that debuted on the DS or 3DS. Only Greninja, Lucario and Lucina debuted on these consoles, which need more representation.
-A colourful cast of characters populate the Layton games, offering interesting alternate costumes, assist trophies and more. And the music would be to die for.
-Layton epitomises the unique staple (3)DS character, and was one of the first franchises to truly explore the touch screen functionality. Liked internally by Nintendo, too; Nintendo UK's website lists him in their character hub, even above the likes of Pikachu and just shy of Link.
-We need a puzzle game representative that isn't Dr. Mario, and actually incorporates puzzle elements. With platformer, adventure, minigame, open-world, arcade, RPG, FPS, fantasy, second life, sports, sci-fi, racing, and even more genres represented, a genuine and hearty foray into the puzzle genre is needed.
-Although third party in Japan, Level-5 and NoJ are very close. Note the availability of the Inazuma Eleven anime on the Nintendo Anime Channel. Layton is a second party character elsewhere published by Nintendo, akin to Pokemon.
-Layton's creators have already stated they would willingly work with the Smash team to make his inclusion a reality.