Personally I believe part of the reason of silence on the internal workings of the ballot is so that they can be more flexible on it. I don't believe there is an exact limit to the number of Sakurai is making, in that it's much like when he's developing the main game: His team manages to make a character quicker than anticipated, or have a personal favorite that they work on during their own time, which results in them deciding more so on an end date than an end amount. I would say 4 is probably the aim, but more is possible. Another reason for the secrecy is freedom. They said after the last characters everything from here on out is fan-service, and that Ryu was the last of the pre-ballot planned characters. Well the code indicates they have 2 characters ingame and working, and those are likely from the ballot. Characters and Stages are different teams, so there's no reason Character development stopped. the Ballot started back in the first of April. The first 2 weeks and the last 1 of any long term event tend to be the strongest. So it's completely possible they chose 2 from the start to begin development, which means it's been about 3 months, and it's to be assumed it takes about 3-5 months to develop 2 characters, possibly less as they streamline.
Personally, I'm expecting 2 more characters before or by the end of the ballot. There is no reason for their not to be in all reality. by the time the ballot ends it will be 6 months since the Ballot started, and 4 Months since the last character. I believe they are still on schedule, and truth be told I doubt Iwata's death has altered that, since Sakurai showed that despite his sadness he wanted to continue working in memory of his friend. Add to that a Smash update video with Sakurai has been done before and can be done again. I still believe our King is likely to be first among them with interesting concepts and the heavy initial and continued support.
Should be interesting to see what happens, but honestly I expect to hear something sooner than later. While I do expect a veteran, I think Newcomers are the focus from here, and I still think it's likely we're getting a NA, EU, JP and Worldwide pick. I also have this kinda feeling that we'll get a newcomer for each, though Wolf will be extra both due to support from the ballot, and the new Star Fox game coming up, and part of the reason they are waiting now is so they can put him in closer to Star Fox Zero's artstyle which would be pretty sick. Here's my thought, you put the ballot out there, what do you really want? old things coming back? or great new ideas and characters from series both new and old? A big part of the ballot is hearing the voice of characters that may have not had a chance otherwise, needless to say our king is up there, but so are those from series with little to no rep like Sami from Advance Wars, or Issac from Goldensun. Throw in the fact that out of the 4 dlc characters so far 3 are vets which is a Japanese focus, and only 2 could be called Global, both with heavy Japanese appeal as well, a stream of newcomers seems likely to me.