Put me on that supporters list, I've been wanting Steve since the first Smash trailer back in March, and I will literally cry if he gets announced. Following the 5chan leak, he and Doomguy would be announced at E3. I can imagine the slash screen appearing, followed by a purple glow, as if looking through glass. The scene changes to Mario, Kirby and Samus, who are trying to discover where that glow comes from, find the Nether portal and enter the it, where they meet face to face with Steve, who watches them enter the new dimension, followed by his splash card "Steve Picks a Fight!'. Then we see Steve's gameplay (I hope he can place blocks or has a crafting mechanic). After that we go back to the trailer, where the four characters fight, while in the distance we hear gunshots. Everyone stops fighting and we see, from top to bottom, how another character has reached the battlefield of Nether, being none other than Doomslayer, with his splash card saying "Doomslayer Tears 'em Up!". The trailer ends there, without showing Doomslayer gameplay. I honestly think it would be a very good way to introduce them both :D
Steve hype!