So we know that there is:
And most likely after today's video:
Hyrule Warriors eventually had 17 playable characters in the base game, plus another 10 from the paid DLC. So that would leave another 7 or so hopefully to be revealed.
Let's hear your predictions for the remaining slots please. I'll get the ball rolling, mine is Pikango. He's an artist in BOTW. I definitely think he has a good chance for inclusion as he would allow for a very creative attack style.