Chance:
50%
The real factor that is holding him back from becoming a DLC fighter is that he is third party character, and Sakurai is pretty strict about third parties when it comes to Smash Bros. Of course, newer Level 5 games that are becoming extremely popular like Yokei Watch, where a Level 5 representative could be used from these games, are another reason why Layton may not make it into Smash Bros.
As for everything else? Personally, I think he has a pretty good shot for a third party character. For starters, all of his games were Nintendo exclusives, being released solely on the Nintendo DS and 3DS respectively. Nintendo and Level-5, though separate video game companies, are on good terms with each other. The Inazuma Eleven anime (which is based on a Level 5 game) appeared on the Nintendo Anime Channel in Japan. More importantly, Nintendo is in charge of distributing the Layton games for the international audience, so you could say he's roughly 40-50% Nintendo in that regard if you take into account that international means "outside of Japan."
Aside from that, Layton actually has a lot of potential for what his moveset can be. Yes, he is a very capable fencer, but there's a lot more to him than that. Throughout the series, he has demonstrated his intellectual genius by creating various gadgets/weapons by combining parts together. To name them all:
- Curious Village: The Custom Glider
- Unwound Future: The Coin-Slot Machine Gun
- Last Specter: The Stone-Launching Catapult
- Eternal Diva (the Layton movie): The Man-Made Helicopter
- Azran Legacy: The Fossil Glider
See where this is going? One can create Layton's special moveset based around all of the inventions and weapons he has created. There are many more he makes throughout the series, mainly for the important puzzles, but those five I have mentioned are the most notable.
Speaking of puzzles, one can create a moveset for Layton based around the puzzles he solves throughout the series. The hint coins he finds and uses can also be incorporated into his moveset very nicely as well; for instance, they could pop up out of the ground and lead to some sort of a counter-move.
Professor Layton has also been a solidly requested character for Smash Bros over the past few years from what I've seen. Even the creators of the Layton games admitted they would love to see Layton appear in Super Smash Bros as a playable fighter.
There has also been a growing female audience for the Layton series. In fact, the games have been well targeted towards them that it's the reason why there are voice actors and actresses for the games. That being said, Professor Layton's inclusion into Smash Bros would be a great way to bring female gamers to the Smash Bros scene.
Want:
100%
Professor Layton is the character I want to see the most in Super Smash Bros. I just see so much potential to what he will bring that I think he'd a worthy addition to the Smash Bros roster. I'm also a huge fan of the Professor Layton series, being very familiar with all of its games, and when I first learned about Smash Bros 4, I remember thinking of how well he could work in the roster. If I see his reveal into Smash Bros become a reality, it'll be the happiest day in my life! His reveal trailer would be the one trailer I would absolutely scream with excitement over, practically as loud as everyone else's reactions when they learned Mewtwo was going to appear as DLC.
Nominations:
I really don't have much in terms of supporting other characters that are currently on the list. In fact, my nominations are going to go to two characters who I really want to see in Smash Bros, but have slim chances compared to most of the other fighters that have been listed. Regardless, I'm still going to nominate them because there is a glimmer of hope within me that wants to see them appear as DLC fighters, and they are the only other fighters I'm interested in for Smash Bros aside from Professor Layton.
Jean Descole: x3 (Descole is the main villain of the second trilogy of the Layton games and very capable fighter in all levels)
Gallade: x2 (Gallade is a Pokemon, my favorite as well, that first appeared in the Pokemon Diamond/Pearl games who recently got a real cool-looking mega-evolution in OR/AS. He is the split evolution of Gardevoir and is a Psychic/Fighting type.)