Hi everyone, long time since I've been around here, but I thought I’d post a theory that’s been bouncing in my head for a long time now: that the original design for Gouki had no Shun Goku Satsu. This move, much like Gouki himself, was a result of fan misinformation that Capcom decided to incorporate into canon. What we saw in SSF2T was not intended to be a special move of any sort, but rather a simple portrayal of Gouki and Vega BOTH fighting EACH OTHER in an intense battle, with Gouki ending up the victor and then turning around to face the player.
Why do I think this? Let’s think carefully about the official canon that was initially given (as stated in the plot guide): Gouki crashed the SF2 tournament, and attacked Vega, who was caught off guard and killed by the SGS. Keep in mind these are from official statements released well after the game.
If this was what was intended when the scene was first made, I believe that the scene would have been portrayed very differently. First, in SSF2T, Gouki approaches from the front, from way behind the player, not behind Vega. It is not portrayed in any way as being sneaky or hard to see coming, and that would be WAY out of character for Gouki anyway. With SF4, this “off guard” idea was then retroactively adjusted to Vega purposely taking the SGS with a contingency plan to be moved to another body again. However, it’s still implied that it “looked” like Vega was caught by surprise and only Vega knew he had a backup body ready. Again, this does not match up well with how the scene was portrayed (not to mention the new statement has Vega’s body being “powderized” which also doesn’t match the original scene), suggesting that it was all tacked on after the fact, once Capcom got the idea of the SGS from fan reactions.
Also note that the animation in this one instance is different from later incarnations of the SGS in a very important way: Gouki did not grab Vega prior to the flash. In every later instance of the SGS, Akuma is clearly shown grabbing the opponent before the move begins. But in this, the first showing, he teleported in, then stopped in front of Vega, both facing each other in their fighting stances, then the screen flashed white and we see the impacts. In other words, it was not originally a grab. Only after the fans mistook it for a super, and Capcom decided to go along with it, did they tack on the grabbing animation which has been present in every single version of the SGS ever since then.
Another point of interest is that Gouki has no super in SSF2T. This is the game that basically brought supers to the series, plus they already have the animations for this move. Gouki was never made in any way to be balanced or fair at all, so why would they not give him his signature move as an incredibly OP super? Simple, because in the creator’s heads, it wasn’t a move. It was a scene where Gouki and Vega are fighting an intense battle.