I don't know how suitable this thread is to exist on the Newcomer Speculation tab, but if you want my prediction on how the characters will be released is this:
October Nintendo Direct: Shadow confirmed as Sonic Echo, Bandana Dee confirmed as playable fighter.
Random trailer revealing Karate Joe from Rhythm Heaven appears on Nintendo's YouTube
November (Smash?) Direct: Dry Bowser, Dixie Kong, and Impa confirmed as Bowser, Diddy Kong, and Sheik Echoes, respectively. We would also see Incineroar's reveal as a playable fighter, and Geno is revealed as an assist trophy. More returning assist trophies are revealed, but Geno's would be more produced, due to him only previously appearing as a Mii costume.
Trailer a week before launch showcasing the big reveal: Isaac from Golden Sun finally got into Smash 5.
Game released.
This is not a leak in any means, but I predict a timeline of character releases similar to something like this. Two more directs before game release, with one being focused on Smash and the (Spirits?) mode. I would assume there will be no more than 4 new characters, and echoes are sprinkled throughout the news. Maybe a few trailers here and there, which I included.
Ah well, I'm probably breaking one of the Smashboards rules, and if I am, I apologize.