Hello! I wanted to share some juicy info I stumbled upon when browsing Game Faqs, regarding the the ballot winners.
http://www.gamefaqs.com/boards/633202-super-smash-bros-for-wii-u/73017398/839638290
http://www.gamefaqs.com/boards/633202-super-smash-bros-for-wii-u/73017398/839639658
Basically, the user named
Kyoskue, claimed that he is a marketing specialist whose team was hired by Nintendo during the campaign of Smash Bros. 3DS/Wii U. The account he is using is not his but from a friend who lend it to him to protect his identity in case he was violating his NDA agreement. He is pretty much sharing some info about how the ballot characters came to be and that Corrin was basically added as advertisement for Fates; he claims he knows this due to having access to text documents during the marketing campaign and throughout his relationship with Nintendo. I recommend you to take a read to those links, and if you want more you can browse the thread he was posting in for additional info.
Of course, due to the nature of this claims there is no real way to prove he is the real deal, but what he says makes a lot of sense and it's better than the rants of "the ballot is a lie because my character didn't make it in" posts, and if it is true, then Corrin's addition wasn't added due to Sakurai bias but because Nintendo pushed for it. So this one isn't on Sakurai, again if true, and people oughta cut him some slack (They won't regardless, because hatedoms are like that).