Considering how much attention Yoshi new Island received in the previous directs, I don't think it's ompossible to get Yoshi tomorrow. I think it is fairly likely and I am banking on him being revealed.
Not to mention the update will be on Friday and is within the 12th and 13th which is generally when we get some type of character reveal outside of a game release
Case in point:
Olimar - 7/12
Luigi - 8/07
Peach - 9/12
Marth - 11/07
King Dedede - 01/10
Little Mac - 02/14
That is usually within the span of a week and around the date of when the game was revealed at E3. Yoshi's game has the convenience of being released within this time frame.
Note: Today is Thursday morning for me. Tomorrow will be Friday.
I think the issue here is NA as opposed to JP reveal.
Now, I understand Diddy. But let's put it this way.
Little Mac was revealed on the supposed date TF was on.
It could've been just an excuse to reveal him.
Here? There's no excuse.
And, we know that Sakurai focuses on Japan releases.
Remember Zelda? She wasn't revealed in November (America's date), but instead December (Japan's date).
But, if anything, it'll either go one or the other.
Yoshi, or Pokemon.
And, since we're running on Japan time. We'll know tomorrow (or Friday, which is our release)...