Every time someone tries to force sales into an argument for or against a character's inclusion, I sigh.
Sure, I'll give you that more sales means more familiarity, more people know about and get excited over the character, they don't have to be big super Nintendo fans to feel included blah blah blah I've heard this song and dance way too much. But as much merit as that does give certain characters, trying to make sales the most important deciding factor on whether or not the character should be in Smash does a great disservice to other great potential characters from lesser-known games. I mean, look at some of the obscure / not super well-known characters already in Smash (being well-known BECAUSE of Smash doesn't count):
Aside from the region-exclusive characters (Lucas, Roy, Marth initially), meaning they're not super well-known by virtue of not being known worldwide, not many people were all that familiar with these characters before Smash escalated their popularity. The F-Zero games were losing popularity due to Mario Kart starting to become the de facto racing game Nintendo would heavily promote instead, the Game & Watches were barely mentioned by the time Melee came out even with the Game & Watch Gallery compilations on the Game Boy, Ice Climber was one very early game with no sequels that sold okay but wasn't super-remembered, Fire Emblem: Path of Radiance sold okay but not great, EarthBound was a flop in America, R.O.B. wasn't even really a video game character and his only two games were unpopular because R.O.B. wasn't a a very reliable peripheral, and similarly to Ike's game, Xenoblade Chronicles sold okay but not great, even if it was touted as the best Operation Rainfall game it still didn't reach a super-wide audience, becoming more of a cult hit even if Operation Rainfall and its success was heavily publicized.
But none of that matters, because every single one of these characters is a blast to play in Smash. Even if my mom or little sister doesn't know who any of these characters are, they're still fun as hell and play satisfyingly in the Smash environment, since even they find themselves enjoying them despite not being familiar with them. It doesn't hurt that most of those characters I listed has a small but passionate fanbase for their games.
People really need to stop being obnoxious about sales. A good character choice is a good character choice, stop measuring sales d*cks for your cult hit character's game versus their cult hit character's game, because at the end of the day they're both not super-popular, and that means both of your characters will be less-known than other characters like Mario or Link or Kirby or Fox. Your non-gamer uncle will still have no idea who the hell Ike or Shulk are. One underground character being slightly more popular than another underground character won't always amount to much, so stop focusing so often on an aspect of a character's game that isn't the end-all be-all.
Smash is supposed to be a celebration of Nintendo, not a Hall of Fame like @
Scoliosis Jones
mentioned. The most popular characters aren't the only ones that make it in, and there's a good reason for that.
/endrant