We haven't gotten anything before at events that aren't directly from Nintendo, and not even always then. I don't think we'll get a reveal from Evo, but it'd be cool if we did.
Besides that, it also depends what would make the most sense. Some are predicting Heihachi there. IMO, I think a Fighting Game character shown off there is a good time for any character, but only if there is one they want to show off there. I also don't think he's that likely, as Sakurai turned him over before because he couldn't think of a moveset that was interesting. Seeing his gameplay, he's a simple martial artist, and while a cool character, my guess is he couldn't find a mechanic to work in. He had similar trouble with Ryu till the unique control method option came in(Traditional Fighting Game controls. I forget what Sakurai outright called his mechanic). I'm not going to call the character boring, cause that's unfair. But when you have someone who is a basic martial artist, you might not get easy inspiration. For instance, Fox is a martial artist too, but he already had more than that. This can hurt Heihachi's chances. They're not dead until we know otherwise, of course.