I know this is a stretch, but I have an extra idea to add to that DLC idea.
Being a huge fighting game fan and being a veteran of many different titles, I've seen many different ways that companies have incorporated extra characters into their games. While there are good ones (Like Skullgirls) there is always bad ones (Like Street Fighter X Tekken). So...what about a vote?
A vote for a total of four characters, two being able to be voted on by North America and Europe while the other two revolve around Japan. The two characters to be voted for would be most overall wanted Nintendo characters and the most-wanted new IP to be represented in Smash Bros. Say if someone big didn't get into Smash Bros that many people wanted in North America but no so much in Japan and vice versa, well then you can vote for said character to try and get them in the game. As for the second one, it's a vote for whatever franchise hasn't been represented in Smash Bros yet. So if Starfy doesn't get in, Japan's vote would most likely be that of the Starfy series, and if Isaac or Shulk doesn't get in, North America's vote could be either Golden Sun or Xenoblade. If it's done that way, it's fair game and it's a fan-input.
Any thoughts on an idea like this?