Sorry about the double posts, but this one is so different I thought it was best to separate it.
Personally, I think Professor Layton is the most Underrated character for Smash DLC. Sure, he's kinda popular, but never really considered among the big hitters, in both want and chance. Despite this, I think he is a very likely DLC character, as well as a great choice.
The main reason I think Layton is likely is that he is the only character who we have probable evidence for getting in. Chris Miller, Layton's English Voice Actor, said on Twitter a while ago (you may remember the whole kerfuffle) that he thought he had voiced lines for smash. This went 'viral' very quickly, causing Miller to retract the statement, and saying he didn't know for sure, but hoped he was in. The most important part of this though, and the part that most people don't know, is that Miller said, in a more private way on twitter, that he had done two voice acting sessions for Layton which he didn't know the reason for. Since the Layton series has ended, this means it must have been for other games, one likely candidate of which is Smash. No other character had evidence as strong as this, yet people rank their chances higher.
Secondly, Layton has many other factors which increase his probability. Despite the fact he's third party, Level 5 has a very strong relationship with Nintendo, as evidenced by the recent push for Yokai Watch. On top of this, many of Level 5's games are Nintendo exclusives, including all of the main series Layton games. Nintendo even published them in North America and Europe. Layton is also an iconic figure in terms of the DS, an underrepresented console in smash. Layton was even included in the booklet showcasing mainly first party games in DS cases, as well as being almost front and center on the European Nintendo site for a while.
Many people bring Layton's 'lack of iconic status' into the fold, but I feel that Layton has enough support for Sakurai to consider him in the ballot, as well as enough affiliation with Nintendo to get around this.
Some other, more minor points include the fact that the Layton games are shown to be more popular than average among female gamers, which may be something Sakurai is looking to encourage (as shown by the fact you have to select your gender in the ballot). Also, Layton is popular all around the world, even being rated among the top video game characters in Japan a couple of years ago, and making Layton seem more likely than characters such as Shovel Knight (whose game hasn't realeased in Japan, not to mention only having one, non-exclusive game). Level 5 has also expressed interest in having Layton in Smash, as well as both Iwata and Miyamoto saying that they like the series.
Overall, I think I have shown here why Layton is, in my opinion, a very underrated character. Please feel free to argue against what I've said, I would like to hear any other opinions on the matter.