I think people are going about it the wrong way if they're trying to dig out individual characters who will "appeal to everyone." There are absolutely characters who will appeal to people more than others, and that should 100% be a consideration where the ballot is concerned. However, I think the better approach is to look at DLC as a package, and depending on who ultimately gets the last few spots, Sakurai and co. will have done a pretty bang-up job at adding in "something for everyone."
You have characters for the nostalgic Smash fans who enjoyed previous games, like Mewtwo and Lucas.
You have characters for the more casual Smash fans who are big into memes, like Roy and his T3h Ph1r3.
You have characters who appeal to fans of the fighting game genre, like Ryu.
You have characters who appeal to the ZOMG HYPE WTF BBQ crowd who suggest off-the-wall characters, like Cloud.
The missing pieces you can add here are the more hardcore Nintendo fans and "the casuals," so to speak. The former, you can appeal to by picking one or two of the characters they voted for in the ballot, and the latter, you can appeal to by putting out flashy and fun-looking characters, probably from newer games. The caveats to consider are that 1) hardcore fans aren't a perfect representation of the fanbase as a whole and 2) casuals aren't the ones who will generally care about DLC and/or still be playing Smash over a year after release.
they popped up first. 
