So Masahiro Sakurai explained the DLC choices for Cloud, Corrin, and Bayonetta on Famitsu. It was fan-translated, so out of respect for the website's wishes, I'm gonna summarize it.
For Cloud, he mentioned that always wanted a Final Fantasy representative in Smash 4. He talked mostly about the character's playstyle.
For Corrin, Sakurai wanted to use a character from an upcoming Nintendo game. He used Fire Emblem Fates, which is already out in Japan and soon to be released overtime, becoming the prime candidate. He thought having too many Fire Emblem characters was going to be a problem (which I know everyone is sick of), but he decided to make Corrin a fun character that is different from other FE characters. Then, he talked about his playstyle, such as being a long-ranged character and a shape-shifter.
For Bayonetta: Now we all know that Bayonetta is the only character that was part of the Smash Ballot. He mentioned that of the 1.8 million votes, Bayonetta had the most out of them. Also, since Bayonetta 2 is a Nintendo exclusive, the negotiations between him and Platinum were very easy. The problem was that he was trying to figure out how to properly represent this character. The best way of doing that is by making her a combo-heavy character, which he went into detail with the playstyle.
One more thing he put out: he mentioned that it was extremely difficult to go through the rating system for each region because of Bayonetta's sexy antics, which was considered strict for Japan's rating board.
Source:
http://www.sourcegaming.info/2015/12/23/496/
