Similarly to what was stated earlier, the only way I could possibly conceive that this leak could be real would be sakurai's statement about showing off the design of every character before launch, which would also address the ridiculous pace of reveals they have had.
So far every character that has been shown off seemed fully complete, and with the pace that they had been going at with characters for the past 5 years, having so many more to do would require a lot more time to finish them for release. This would also address the matter of Sakurai's statement regarding their possible mistake in the pace of their reveals.
My biggest provider of doubt however, must be the fact that his first statements regarding new characters was to "not expect too many" which makes the current number plus 2-3 more seem like the most likely scenario.
Granted, if this leak is real, I would consider it the best timeline, even with the inclusion of chorus kids. (I'm sorry, but I have never played rhythm heaven and I just can't stand their design).