If I had to make a guess for who's going to appear...
At E3, Brave will be a Dragon Quest character. I'm thinking Slime, though it could be Erdrick or the Luminary. DQ Char will be revealed alongside 3, but released shortly after E3 as opposed to number 3, who will come at around very early October. The third character will probably be the big reveal for casual audiences: I honest to god think The Human from Undertale is happening.
Since I don't believe Costume Theory, I expect that at later dates, Crash and as the final character, either Banjo or Steve, will show up. If Costume Theory doesn't go the way of music but instead box, then I'd put money on Lloyd Irving and either Dante or an RE character.