Rest assured, Gogo's mystery remains intact. All that has changed was the translation.
I never did think of that for the Daryl theory though...amnesia. It sure is a recurring theme in role playing games anyway, and if such were to be the case, it would explain the hum...disposition by which Gogo abides. Always ''off'' and cooky...but then, would Setzer not recognize the voice?
The Banon theory seems to stem from the very image you posted. People like to theorize that the little you can see of Gogo's eyes resemble that on Banon's, that as well as the position in which they both stand in the artworks. But that is a bit loose to base anything on...I have never really noticed it myself.
...also, Banon was the leader of the Returners. Were he to still be alive, would he not want to continue the battle against the empire?
Of course, the empire no longer exists after that, however let it be noted that while Banon's rebellion movement seemed rather patriotic, one can tell that his true intent was for a peaceful world, so I believe that he would still fight against Kefka...of course he still does, in a way, if he is indeed Gogo. That does not explain the new found miming abilities though.
Incidentally, some people tend to think That Arvis is Gogo, as well.
Hmm...Relm's parents...well, it is proven, pretty much anyways, that Clyde is indeed Relm's father...so that would mean that Gogo would have to be a women. Also, is not Strago Relm's grandfather? That means that Shadow is his son?
Or also, there is the ever returning theory that Gogo is General Leo.
O_o
Right, Gogo was a very useful character. Miming came quite handy, however it seems that he is always slightly weaker...if you mime Bum Rush for example, Sabin will deal 9999 damage, but Gogo will do a little less. Since you get him so late, there is little time to upgrade his statistics with the Espers though, which would probably boost him a little.
But his damned supposed Desperation Attack, Meteo X, I NEVER did manage to unleash.