The only characters I can really see being announced on or before the release are character not on the roster. They've never once had two trailers for the same franchise, so I'd find it questionable to see any of the other unlockables save Duck Hunt shown off in a trailer (and I'm sure we WILL get one more trailer) before release. Now, other characters will probably have an intro, but not a full-on trailer. Duck Hunt probably won't have a trailer either.
The only characters I can see getting trailers are newcomers from franchises that haven't gotten a newcomer trailer or a new franchise that isn't Duck Hunt (because clearly he's this game's Game and Watch/ROB).
Agreed. Duck Hunt is our Mr. Game & Watch/R.O.B.
When was it said there would be a character reveal?
I remember the NicoNico thing saying there was a new character, but I believe that was a mistranslation, and the NoA Treehouse stream said no such thing at all.
No confirmation of any trailers at all during the streams. In fact, I doubt they will have trailers. But Sakurai never said Shulk was the final trailer, so I highly doubt he is. I'd be surprised if we didn't get a trailer on launch, but it probably wouldn't be in either of the streams. Ridley, K. Rool, and Mewtwo are a prime example of the possibility, they'd be the most hype. Isaac is a slim possibility, and out of all the characters still fairly likely to be in, he's the only one who would fit in the roster without MAJOR revisions to the roster.
I still say if he's in, K. Rool is more likely than Ridley to be announced, but a Big 3 trailer would be the best bet.