To me, it feels like that started shifting around the time of brawl. Sure, I can understand people thinking there can be too many third parties... but whats the problem? Most of the ones that do get in are icons in their own right. To me, Smash has always felt less like a Nintendo All-star title nowadays (like it was back in the first two), and more like a celebration of gaming. Gaming icons from every walk of life battling it out... All of the third parties so far have been icons. Sonic, Pacman, and Megaman both represent their companies and their styles well. (and Ryu will represent the classic style of the classic fighting games..)
So, why should it matter? As we have went over there is no just thing as "slots" here. No one is stealing the space of any character. That is just a paranoid concept the fans created. Nothing more
..
Anyway, who is to say we'll end up with a ton of 3rd parties?... So far there is what? Four third parties?.. That's 4 to 48 first party characters (4 to 51 if you count the mii fighters). Lets say that number doubled by Smash five.. that would be 8 third parties.. of course, that wouldn't be nearly as bad, as the other side usually doubles as well. So that would be an additional 4 to what? 10 or 15 newcomers?
Now if it were like say, 30 third parties to 20, then yes, I would be kinda irritated. However that isn't the case... there has never been an instance thus far where third party characters have outnumbered the first party, and I doubt there ever will be.
All that said, why should it matter? I believe the only reason many players fear 3rd parties in the ballot (and usually Smash in general) is due to the slot mindset.. Whats sad, is I've seen many grow an unfounded hatred for some characters because of this stuff.. Some of us can't bare the thought of our favorite character "being shown up" by a character we don't like.
At any rate... There is no need to step on third party campaigns, just for what company owns the character. I garantee you if Bandana Waddle Dee weren't owned by Nintendo and had say, been bought out by like... Activision (I know it would never happen XD, but it's just an example), detractors would swarm this thread like it's the plague shouting "B DEE IS THIRD PARTY. HE'LL NEVER BE IN SMASH."
...The point is, lets not step all over third parties/indies, shall we? They have fanbases that would love to be able to main those characters just as much as many of you want to main the Dee.