Adding a Dragon Quest character just because it's a really popular franchise that's still going isn't a good enough reason to add a character from it into Smash in my opinion. Mainly because there isn't really a super popular character they could add from Dragon Quest that would attract a large audience.
There's a new main character every game ,and they're kind of blank slates, and not all that popular or memorable. Final Fantasy also get's a new main protagonist every game, but they are their own established and unique characters that people love. Final Fantasy has main protagonists like Cloud, Squall, Tidus, Cecil, etc. Dragon Quest has main protagonists like Hero, Hero, Hero, Hero, etc.
The only character from DQ that I would say is really iconic is the Slime enemy, and I doubt they would add a character like Slime into Smash, because of his status as a generic enemy. There is a reason we got an established character like Cloud in Smash over a generic Chocobo or Moogle.
I think the character themselves are more important than the series they come from. Someone like Geno would probably garner more interest than any of the characters Dragon Quest has to offer. Outside of Japan anyway.
That's another thing; while Dragon Quest is absurdly popular in Japan it's reception in the west is nowhere close to matching it. All of the games have sold significantly more in Japan than the rest of the world combined, and when you consider just how small Japan is that's kind of sad.
Maybe the people in Japan would absolutely love generic Hero or generic Slime to be in Smash, but if they want the 3rd party characters to appeal to a worldwide audience I don't think it's a good idea.
Man this went on longer than I intended.
